Method for transmitting discovery message in wireless communication system and method for same

ABSTRACT

The present invention discloses a method for transmitting a discovery message in a wireless communication system and an apparatus for the method. More specifically, a method for transmitting a discovery message in a wireless communication system supporting communication between user equipments (UEs) comprises estimating, by a UE, an energy level over an energy detection interval configured within a discovery resource pool; determining, by the UE, a discovery resource region of the UE on the basis of the estimated energy level; selecting, by the UE, a discovery resource for transmitting a discovery message within the determined discovery resource region; and transmitting, by the UE, the discovery message from the selected discovery resource.

TECHNICAL FIELD

The present invention relates to a wireless communication system and,more particularly, to a method for transmitting a discovery message in awireless communication system supporting communication between userequipments and an apparatus supporting the same.

BACKGROUND ART

Mobile communication systems have been developed to provide voiceservices, while guaranteeing user activity. Service coverage of mobilecommunication systems, however, has extended even to data services, aswell as voice services, and currently, an explosive increase in traffichas resulted in shortage of resource and user demand for a high speedservices, requiring advanced mobile communication systems.

The requirements of the next-generation mobile communication system mayinclude supporting huge data traffic, a remarkable increase in thetransfer rate of each user, the accommodation of a significantlyincreased number of connection devices, very low end-to-end latency, andhigh energy efficiency. To this end, various techniques, such as smallcell enhancement, dual connectivity, massive Multiple Input MultipleOutput (MIMO), in-band full duplex, non-orthogonal multiple access(NOMA), supporting super-wide band, and device networking, have beenresearched.

DISCLOSURE Technical Problem

In device to device communication, a distributed discovery methodincludes sensing, by all devices, the entire D2D discovery resource poolin a lump in order to select discovery resources. This increases adevice processing load and is not suitable for discovering an adjacentdevice.

To solve the technical problem above, the present invention provides amethod for a UE to determine a discovery resource region adaptively onthe basis of an estimated energy level over a predetermined energydetection interval and to transmit a discovery message by usingdiscovery resources selected within the determined discovery resourceregion; and an apparatus for the method in a wireless communicationsystem supporting device-to-device (D2D) communication.

Also, the present invention provides a method for dividing one discoveryresource pool into a plurality of time slots, determining a discoveryresource region adaptively for a UE for each time slot on the basis ofan estimated energy level over an energy detection interval set for thetime slot, and transmitting a discovery message by using discoveryresources selected within the determined discovery resource region; andan apparatus for the method.

The technical problems solved by the present invention are not limitedto the above technical problems and those skilled in the art mayunderstand other technical problems from the following description.

Technical Solution

According to one aspect of the present invention, a method fortransmitting a discovery message in a wireless communication systemsupporting communication between user equipments (UEs) comprisesestimating, by a UE, an energy level over an energy detection intervalconfigured within a discovery resource pool; determining, by the UE, adiscovery resource region of the UE on the basis of the estimated energylevel; selecting, by the UE, a discovery resource for transmitting adiscovery message within the determined discovery resource region; andtransmitting, by the UE, the discovery message from the selecteddiscovery resource.

According to one aspect of the present invention, a user equipment (UE)transmitting a discovery message in a wireless communication systemsupporting communication between UEs, comprises a Radio Frequency (RF)unit for transmitting and receiving a radio signal; and a processor,wherein the processor is configured to estimate an energy level over anenergy detection interval configured within a discovery resource pool,to determine a discovery resource region of the UE on the basis of theestimated energy level, to select a discovery resource for transmittinga discovery message within the determined discovery resource region, andto transmit the discovery message from the selected discovery resource.

Preferably, the discovery message resource region can be adaptivelyconfigured to one region or a combination of two or more regions fromamong frequency domain, time domain, and spatial domain within thediscovery resource pool.

Preferably, the UE can sense the determined discovery resource regionand arbitrarily select the discovery resource from among the resourcesof which the energy level falls within a predetermine range.

Preferably, the energy detection interval can comprise one or moresubframes, or one or more symbol intervals.

Preferably, size of the discovery resource region can be determined onthe basis of the estimated energy level, and a location of the discoveryresource region can be randomly determined by using the UE identifier.

Preferably, the discovery resource pool can be divided into a pluralityof time slots, and the energy detection interval can be configured foreach of the plurality of time slots.

Preferably, the discovery resource region can be determinedindependently for each of the plurality of time slots.

Preferably, the discovery resource can be selected by sensing only partof the discovery resource regions from among the discovery resourceregions configured for each of the plurality of time slots.

Preferably, in case the UE starts sensing one of the discovery resourceregions from among the discovery resource regions configured for each ofthe plurality of time slots, the discovery resource is selected withinthe discovery resource region next to the discovery resource region overwhich the UE has started sensing.

Advantageous Effects

According to an embodiment of the present invention, sensing power of aUE can be reduced as the UE determines a discovery resource regionadaptively on the basis of an energy level estimated over apredetermined energy detection interval.

Also, as a UE determines a discovery resource region adaptively on thebasis of an energy level estimated over a predetermined energy detectioninterval, overhead due to a sensing process can be reduced efficiently.

Also, as a UE determines a discovery resource region for each time slotadaptively on the basis of an energy level estimated over an energydetection interval set for the time slot, all of the time slots are notnecessarily sensed, and therefore, energy consumed for D2D discovery canbe reduced.

Also, since discovery resources are sensed and selected in a selectivemanner even if UEs start sensing in the middle of a discovery resourcepool, delay in the discovery procedure can be reduced.

The effects of the present invention are not limited to theabove-described effects and other effects which are not described hereinwill become apparent to those skilled in the art from the followingdescription.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention.

FIG. 1 shows the structure of a radio frame in a wireless communicationsystem to which an embodiment of the present invention may be applied.

FIG. 2 is a diagram illustrating a resource grid for one downlink slotin a wireless communication system to which an embodiment of the presentinvention may be applied.

FIG. 3 shows the structure of a downlink subframe in a wirelesscommunication system to which an embodiment of the present invention maybe applied.

FIG. 4 shows the structure of an uplink subframe in a wirelesscommunication system to which an embodiment of the present invention maybe applied.

FIG. 5 shows an example of a form in which PUCCH formats are mapped tothe PUCCH region of the uplink physical resource block in a wirelesscommunication system to which an embodiment of the present invention maybe applied.

FIG. 6 shows the structure of a CQI channel in the case of a normal CPin a wireless communication system to which an embodiment of the presentinvention may be applied.

FIG. 7 shows the structure of an ACK/NACK channel in the case of anormal CP in a wireless communication system to which an embodiment ofthe present invention may be applied.

FIG. 8 shows an example in which five SC-FDMA symbols are generated andtransmitted during one slot in a wireless communication system to whichan embodiment of the present invention may be applied.

FIG. 9 shows an example of component carriers and a carrier aggregationin a wireless communication system to which an embodiment of the presentinvention may be applied.

FIG. 10 shows an example of the structure of a subframe according tocross-carrier scheduling in a wireless communication system to which anembodiment of the present invention may be applied.

FIG. 11 shows an example of transport channel processing for an UL-SCHin a wireless communication system to which an embodiment of the presentinvention may be applied.

FIG. 12 shows an example of a signal processing process in an uplinkshared channel, that is, a transport channel, in a wirelesscommunication system to which an embodiment of the present invention maybe applied.

FIG. 13 shows the configuration of a known MIMO communication system.

FIG. 14 is a diagram showing a channel from a plurality of transmissionantennas to a single reception antenna.

FIG. 15 illustrates a reference signal pattern mapped to a downlinkresource block pair in a wireless communication system to which anembodiment of the present invention may be applied.

FIG. 16 illustrates an uplink subframe including sounding referencesignal symbols in a wireless communication system to which an embodimentof the present invention may be applied.

FIG. 17 illustrates the segmentation of a relay node resource in awireless communication system to which an embodiment of the presentinvention may be applied.

FIG. 18 is a diagram conceptually illustrating D2D communication in awireless communication system to which an embodiment of the presentinvention may be applied.

FIG. 19 shows an example of various scenarios of D2D communication towhich a method proposed in this specification may be applied.

FIG. 20 shows an example in which discovery resources have beenallocated according to an embodiment of the present invention.

FIG. 21 is a simplified diagram illustrating a discovery processaccording to an embodiment of the present invention.

FIG. 22 illustrates a method for transmitting a D2D discovery messageaccording to one embodiment of the present invention.

FIG. 23 illustrates a method for adaptively determining a discoveryresource region in the frequency domain according to one embodiment ofthe present invention.

FIG. 24 illustrates a method for adaptively determining a discoveryresource region in the time domain according to one embodiment of thepresent invention.

FIG. 25 illustrates an energy detection interval set in the time domainin a repetitive manner according to one embodiment of the presentinvention.

FIG. 26 illustrates a method for adaptively determining a discoveryresource region in the frequency domain in case an energy detectioninterval is set repeatedly in the time domain according to oneembodiment of the present invention.

FIG. 27 illustrates a method for adaptively determining a discoveryresource region in the time domain in case an energy detection intervalis set repeatedly in the time domain according to one embodiment of thepresent invention.

FIG. 28 illustrates a method for adaptively determining a discoveryresource region in the time domain in case an energy detection intervalis set repeatedly in the time domain according to one embodiment of thepresent invention.

FIG. 29 illustrates a method for adaptively determining a discoveryresource region in the time domain in case an energy detection intervalis set repeatedly in the time domain according to one embodiment of thepresent invention.

FIG. 30 illustrates a block diagram of a wireless communication deviceaccording to one embodiment of the present invention.

MODE FOR INVENTION

Some embodiments of the present invention are described in detail withreference to the accompanying drawings. A detailed description to bedisclosed along with the accompanying drawings are intended to describesome exemplary embodiments of the present invention and are not intendedto describe a sole embodiment of the present invention. The followingdetailed description includes more details in order to provide fullunderstanding of the present invention. However, those skilled in theart will understand that the present invention may be implementedwithout such more details.

In some cases, in order to avoid that the concept of the presentinvention becomes vague, known structures and devices are omitted or maybe shown in a block diagram form based on the core functions of eachstructure and device.

In this specification, a base station has the meaning of a terminal nodeof a network over which the base station directly communicates with adevice. In this document, a specific operation that is described to beperformed by a base station may be performed by an upper node of thebase station according to circumstances. That is, it is evident that ina network including a plurality of network nodes including a basestation, various operations performed for communication with a devicemay be performed by the base station or other network nodes other thanthe base station. The base station (BS) may be substituted with anotherterm, such as a fixed station, a Node B, an eNB (evolved-NodeB), a BaseTransceiver System (BTS), or an access point (AP). Furthermore, thedevice may be fixed or may have mobility and may be substituted withanother term, such as User Equipment (UE), a Mobile Station (MS), a UserTerminal (UT), a Mobile Subscriber Station (MSS), a Subscriber Station(SS), an Advanced Mobile Station (AMS), a Wireless Terminal (WT), aMachine-Type Communication (MTC) device, a Machine-to-Machine (M2M)device, or a Device-to-Device (D2D) device.

Hereinafter, downlink (DL) means communication from an eNB to UE, anduplink (UL) means communication from UE to an eNB. In DL, a transmittermay be part of an eNB, and a receiver may be part of UE. In UL, atransmitter may be part of UE, and a receiver may be part of an eNB.

Specific terms used in the following description have been provided tohelp understanding of the present invention, and the use of suchspecific terms may be changed in various forms without departing fromthe technical sprit of the present invention.

The following technologies may be used in a variety of wirelesscommunication systems, such as Code Division Multiple Access (CDMA),Frequency Division Multiple Access (FDMA), Time Division Multiple Access(TDMA), Orthogonal Frequency Division Multiple Access (OFDMA), SingleCarrier Frequency Division Multiple Access (SC-FDMA), and Non-OrthogonalMultiple Access (NOMA). CDMA may be implemented using a radiotechnology, such as Universal Terrestrial Radio Access (UTRA) orCDMA2000. TDMA may be implemented using a radio technology, such asGlobal System for Mobile communications (GSM)/General Packet RadioService (GPRS)/Enhanced Data rates for GSM Evolution (EDGE). OFDMA maybe implemented using a radio technology, such as Institute of Electricaland Electronics Engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX),IEEE 802.20, or Evolved UTRA (E-UTRA). UTRA is part of a UniversalMobile Telecommunications System (UMTS). 3rd Generation PartnershipProject (3GPP) Long Term Evolution (LTE) is part of an Evolved UMTS(E-UMTS) using evolved UMTS Terrestrial Radio Access (E-UTRA), and itadopts OFDMA in downlink and adopts SC-FDMA in uplink. LTE-Advanced(LTE-A) is the evolution of 3GPP LTE.

Embodiments of the present invention may be supported by the standarddocuments disclosed in at least one of IEEE 802, 3GPP, and 3GPP2, thatis, radio access systems. That is, steps or portions that belong to theembodiments of the present invention and that are not described in orderto clearly expose the technical spirit of the present invention may besupported by the documents. Furthermore, all terms disclosed in thisdocument may be described by the standard documents.

In order to more clarify a description, 3GPP LTE/LTE-A is chieflydescribed, but the technical characteristics of the present inventionare not limited thereto.

General System to which the Present Invention May be Applied

FIG. 1 shows the structure of a radio frame in a wireless communicationsystem to which an embodiment of the present invention may be applied.

3GPP LTE/LTE-A support a radio frame structure type 1 which may beapplicable to Frequency Division Duplex (FDD) and a radio framestructure which may be applicable to Time Division Duplex (TDD).

FIG. 1(a) illustrates the radio frame structure type 1. A radio frameconsists of 10 subframes. One subframe consists of 2 slots in a timedomain. The time taken to send one subframe is called a TransmissionTime Interval (TTI). For example, one subframe may have a length of 1ms, and one slot may have a length of 0.5 ms.

One slot includes a plurality of Orthogonal Frequency DivisionMultiplexing (OFDM) symbols in the time domain and includes a pluralityof Resource Blocks (RBs) in a frequency domain. In 3GPP LTE, OFDMsymbols are used to represent one symbol period because OFDMA is used indownlink. An OFDM symbol may be called one SC-FDMA symbol or symbolperiod. An RB is a resource allocation unit and includes a plurality ofcontiguous subcarriers in one slot.

FIG. 1(b) illustrates the frame structure type 2. The radio framestructure type 2 consists of 2 half frames. Each of the half framesconsists of 5 subframes, a Downlink Pilot Time Slot (DwPTS), a GuardPeriod (GP), and an Uplink Pilot Time Slot (UpPTS). One subframeconsists of 2 slots. The DwPTS is used for initial cell search,synchronization, or channel estimation in UE. The UpPTS is used forchannel estimation in an eNB and to perform uplink transmissionsynchronization with UE. The guard period is an interval in whichinterference generated in uplink due to the multi-path delay of adownlink signal between uplink and downlink is removed.

In the frame structure type 2 of a TDD system, an uplink-downlinkconfiguration is a rule indicating whether uplink and downlink areallocated (or reserved) to all subframes. Table 1 shows theuplink-downlink configuration.

TABLE 1 DL-to-UL UL-DL Switch- configure- point Subframe number tionperiodicity 0 1 2 3 4 5 6 7 8 9 0 5 ms D S U U U D S U U U 1 5 ms D S UU D D S U U D 2 5 ms D S U D D D S U D D 3 10 ms D S U U U D D D D D 410 ms D S U U D D D D D D 5 10 ms D S U D D D D D D D 6 5 ms D S U U U DS U U D

Referring to Table 1, in each subframe of the radio frame, “D” isindicative of a subframe for downlink transmission, “U” is indicative ofa subframe for uplink transmission, and “S” is indicative of a specialsubframe including three types of a DwPTS, GP, and UpPTS. Anuplink-downlink configuration may be classified into 7 types. Thepositions and/or number of downlink subframes, special subframes, anduplink subframe are different in each configuration.

A point of time at which a change is performed from downlink to uplinkor a point of time at which a change is performed from uplink todownlink is called a switching point. The periodicity of the switchingpoint means a cycle in which an uplink subframe and a downlink subframeare changed is identically repeated. Both 5 ms and 10 ms are supportedin the periodicity of a switching point. If the periodicity of aswitching point has a cycle of a 5 ms downlink-uplink switching point,the special subframe S is present in each half frame. If the periodicityof a switching point has a cycle of a 5 ms downlink-uplink switchingpoint, the special subframe S is present in the first half frame only.

In all the configurations, 0 and 5 subframes and a DwPTS are used foronly downlink transmission. An UpPTS and a subframe subsequent to asubframe are always used for uplink transmission.

Such uplink-downlink configurations may be known to both an eNB and UEas system information. An eNB may notify UE of a change of theuplink-downlink allocation state of a radio frame by transmitting onlythe index of uplink-downlink configuration information to the UEwhenever the uplink-downlink configuration information is changed.Furthermore, configuration information is kind of downlink controlinformation and may be transmitted through a Physical Downlink ControlChannel (PDCCH) like other scheduling information. Configurationinformation may be transmitted to all UEs within a cell through abroadcast channel as broadcasting information.

The structure of a radio frame is only one example. The number ofsubcarriers included in a radio frame or the number of slots included ina subframe and the number of OFDM symbols included in a slot may bechanged in various ways.

FIG. 2 is a diagram illustrating a resource grid for one downlink slotin a wireless communication system to which an embodiment of the presentinvention may be applied.

Referring to FIG. 2, one downlink slot includes a plurality of OFDMsymbols in a time domain. It is described herein that one downlink slotincludes 7 OFDMA symbols and one resource block includes 12 subcarriersfor exemplary purposes only, and the present invention is not limitedthereto.

Each element on the resource grid is referred to as a resource element,and one resource block (RB) includes 12×7 resource elements. The numberof RBs N^(DL) included in a downlink slot depends on a downlinktransmission bandwidth.

The structure of an uplink slot may be the same as that of a downlinkslot.

FIG. 3 shows the structure of a downlink subframe in a wirelesscommunication system to which an embodiment of the present invention maybe applied.

Referring to FIG. 3, a maximum of three OFDM symbols located in a frontportion of a first slot of a subframe correspond to a control region inwhich control channels are allocated, and the remaining OFDM symbolscorrespond to a data region in which a physical downlink shared channel(PDSCH) is allocated. Downlink control channels used in 3GPP LTEinclude, for example, a physical control format indicator channel(PCFICH), a physical downlink control channel (PDCCH), and a physicalhybrid-ARQ indicator channel (PHICH).

A PCFICH is transmitted in the first OFDM symbol of a subframe andcarries information about the number of OFDM symbols (i.e., the size ofa control region) which is used to transmit control channels within thesubframe. A PHICH is a response channel for uplink and carries anacknowledgement (ACK)/not-acknowledgement (NACK) signal for a HybridAutomatic Repeat Request (HARQ). Control information transmitted in aPDCCH is called Downlink Control Information (DCI). DCI includes uplinkresource allocation information, downlink resource allocationinformation, or an uplink transmission (Tx) power control command for aspecific UE group.

A PDCCH may carry information about the resource allocation andtransport format of a downlink shared channel (DL-SCH) (this is alsocalled an “downlink grant”), resource allocation information about anuplink shared channel (UL-SCH) (this is also called a “uplink grant”),paging information on a PCH, system information on a DL-SCH, theresource allocation of a higher layer control message, such as a randomaccess response transmitted on a PDSCH, a set of transmission powercontrol commands for individual UE within specific UE group, and theactivation of a Voice over Internet Protocol (VoIP), etc. A plurality ofPDCCHs may be transmitted within the control region, and UE may monitora plurality of PDCCHs. A PDCCH is transmitted on a single ControlChannel Element (CCE) or an aggregation of some contiguous CCEs. A CCEis a logical allocation unit that is used to provide a PDCCH with acoding rate according to the state of a radio channel. A CCE correspondsto a plurality of resource element groups. The format of a PDCCH and thenumber of available bits of a PDCCH are determined by an associationrelationship between the number of CCEs and a coding rate provided byCCEs.

An eNB determines the format of a PDCCH based on DCI to be transmittedto UE and attaches a Cyclic Redundancy Check (CRC) to controlinformation. A unique identifier (a Radio Network Temporary Identifier(RNTI)) is masked to the CRC depending on the owner or use of a PDCCH.If the PDCCH is a PDCCH for specific UE, an identifier unique to the UE,for example, a Cell-RNTI (C-RNTI) may be masked to the CRC. If the PDCCHis a PDCCH for a paging message, a paging indication identifier, forexample, a Paging-RNTI (P-RNTI) may be masked to the CRC. If the PDCCHis a PDCCH for system information, more specifically, a SystemInformation Block (SIB), a system information identifier, for example, aSystem Information-RNTI (SI-RNTI) may be masked to the CRC. A RandomAccess-RNTI (RA-RNTI) may be masked to the CRC in order to indicate arandom access response which is a response to the transmission of arandom access preamble by UE.

FIG. 4 shows the structure of an uplink subframe in a wirelesscommunication system to which an embodiment of the present invention maybe applied.

Referring to FIG. 4, the uplink subframe may be divided into a controlregion and a data region in a frequency domain. A physical uplinkcontrol channel (PUCCH) carrying uplink control information is allocatedto the control region. A physical uplink shared channel (PUSCH) carryinguser data is allocated to the data region. In order to maintain singlecarrier characteristic, one UE does not send a PUCCH and a PUSCH at thesame time.

A Resource Block (RB) pair is allocated to a PUCCH for one UE within asubframe. RBs belonging to an RB pair occupy different subcarriers ineach of 2 slots. This is called that an RB pair allocated to a PUCCH isfrequency-hopped in a slot boundary.

Physical Uplink Control Channel (PUCCH)

Uplink Control Information (UCI) transmitted through a PUCCH may includea Scheduling Request (SR), HARQ ACK/NACK information, and downlinkchannel measurement information.

HARQ ACK/NACK information may be generated depending on whether adownlink data packet on a PDSCH has been successfully decoded. In anexisting wireless communication system, 1 bit is transmitted as ACK/NACKinformation with respect to the transmission of downlink singlecodeword, and 2 bits are transmission as ACK/NACK information withrespect to the transmission of downlink 2 codewords.

Channel measurement information denotes feedback information related toa Multiple Input Multiple Output (MIMO) scheme and may include a ChannelQuality Indicator (CQI), a Precoding Matrix Index (PMI), and a RankIndicator (RI). Such channel measurement information may be commonlycalled a CQI.

In order to transmit a CQI, 20 bits may be used in each subframe.

A PUCCH may be modulated using a Binary Phase Shift Keying (BPSK) schemeand a Quadrature Phase Shift Keying (QPSK) scheme. Control informationfor a plurality of UEs may be transmitted through a PUCCH. If CodeDivision Multiplexing (CDM) is performed in order to distinguish thesignals of UEs from each other, a Constant Amplitude ZeroAutocorrelation (CAZAC) sequence of a length 12 is mostly used. TheCAZAC sequence has a characteristic in that a constant size (amplitude)is maintained in a time domain and a frequency domain. Accordingly, theCAZAC sequence has a property suitable for increasing coverage bylowering the Peak-to-Average Power Ratio (PAPR) or Cubic Metric (CM) ofUE. Furthermore, ACK/NACK information about downlink data transmissiontransmitted through a PUCCH is covered using an orthogonal sequence oran Orthogonal Cover (OC).

Furthermore, control information transmitted through a PUCCH may bedistinguished from each other using a cyclically shifted sequence havinga different Cyclic Shift (CS) value. The cyclically shifted sequence maybe generated by cyclically shifting a base sequence by a specific CSamount. The specific CS amount is indicated by a CS index. The number ofavailable CSs may be different depending on delay spread of a channel. Avariety of types of sequences may be used as the base sequence, and theCAZAC sequence is an example of the sequences.

Furthermore, the amount of control information that may be transmittedby UE in one subframe may be determined depending on the number ofSC-FDMA symbols which may be used to send the control information (i.e.,SC-FDMA symbols other than SC-FDMA symbols which are used to send aReference Signal (RS) for the coherent detection of a PUCCH).

In a 3GPP LTE system, a PUCCH is defined as a total of 7 differentformats depending on control information that is transmitted, amodulation scheme, and the amount of control information. The attributesof Uplink Control Information (UCI) transmitted according to each PUCCHformat may be summarized as in Table 2 below.

TABLE 2 PUCCH Format Uplink Control Information (UCI) Format 1Scheduling Request (SR) (not-modulated waveform) Format 1a 1-bit HARQACK/NACK with/without SR Format 1b 2-bit HARQ ACK/NACK with/without SRFormat 2 CQI (20 coded bits) Format 2 CQI and 1- or 2-bit HARQ ACK/NACK(20 bits) for extended CP only Format 2a CQI and 1-bit HARQ ACK/NACK(20 + 1 coded bits) Format 2b CQI and 2-bit HARQ ACK/NACK (20 + 2 codedbits)

The PUCCH format 1 is used for SR-only transmission. In the case ofSR-only transmission, a not-modulated waveform is applied. This isdescribed in detail later.

The PUCCH format 1a or 1b is used to send HARQ ACK/NACK. If HARQACK/NACK is solely transmitted in a specific subframe, the PUCCH format1a or 1b may be used. Alternatively, HARQ ACK/NACK and an SR may betransmitted in the same subframe using the PUCCH format 1a or 1b.

The PUCCH format 2 is used to send a CQI, and the PUCCH format 2a or 2bis used to send a CQI and HARQ ACK/NACK.

In the case of an extended CP, the PUCCH format 2 may be used to send aCQI and HARQ ACK/NACK.

FIG. 5 shows an example of a form in which the PUCCH formats are mappedto the PUCCH region of the uplink physical resource block in a wirelesscommunication system to which an embodiment of the present invention maybe applied.

In FIG. 5, N_(RB) ^(UL) is indicative of the number of RBs in uplink,and 0, 1, . . . , N_(RB) ^(UL)−1 means the number of physical RBs.Basically, a PUCCH is mapped to both edges of an uplink frequency block.As shown in FIG. 5, the PUCCH format 2/2a/2b is mapped to a PUCCH regionindicated by m=0, 1. This may represent that the PUCCH format 2/2a/2b ismapped to RBs located at a band edge. Furthermore, the PUCCH format2/2a/2b and the PUCCH format 1/1a/1b may be mixed and mapped to a PUCCHregion indicated by m=2. Furthermore, the PUCCH format 1/1a/1b may bemapped to a PUCCH region indicated by m=3, 4, 5. UEs within a cell maybe notified of the number N_(RB) ⁽²⁾ of PUCCH RBs which may be used bythe PUCCH format 2/2a/2b through broadcasting signaling.

The PUCCH format 2/2a/2b is described below. The PUCCH format 2/2a/2b isa control channel for transmitting channel measurement feedback (i.e., aCQI, a PMI, and an RI).

The report cycle of channel measurement feedback (hereinafter commonlycalled “CQI information”) and a frequency unit (or frequency resolution)to be measured may be controlled by an eNB. In a time domain, a periodicor aperiodic CQI report may be supported. The PUCCH format 2 may be usedfor a periodic report, and a PUSCH may be used for an aperiodic report.In the case of an aperiodic report, an eNB may instruct UE to carry anindividual CQI report on a resource scheduled to transmit uplink data.

FIG. 6 shows the structure of a CQI channel in the case of a normal CPin a wireless communication system to which an embodiment of the presentinvention may be applied.

The SC-FDMA symbols 1 and 5 (i.e., the second and the sixth symbols) ofthe SC-FDMA symbols 0 to 6 of one slot are used to transmit ademodulation reference signal (DMRS), and the remaining SC-FDMA symbolsof the SC-FDMA symbols 0 to 6 of the slot may be used to CQIinformation. Meanwhile, in the case of an extended CP, one SC-FDMAsymbol (SC-FDMA symbol 3) is used for DMRS transmission.

In the PUCCH format 2/2a/2b, modulation by a CAZAC sequence issupported, and a QPSK-modulated symbol is multiplied by a CAZAC sequenceof a length 12. A Cyclic Shift (CS) of the sequence is changed between asymbol and a slot. Orthogonal covering is used for a DMRS.

A reference signal (DMRS) is carried on 2 SC-FDMA symbols that belong to7 SC-FDMA symbols included in one slot and that is spaced at 3 SC-FDMAsymbols. CQI information is carried on the remaining 5 SC-FDMA symbolsof the 7 SC-FDMA symbols. Two RSs are used in one slot in order tosupport high-speed UE. Furthermore, UEs are distinguished from eachother using Cyclic Shift (CS) sequences. CQI information symbols aremodulated into all SC-FDMA symbols and transferred. The SC-FDMA symbolsconsist of one sequence. That is, UE modulates a CQI using each sequenceand sends the CQI.

The number of symbols which may be transmitted in one TTI is 10, and themodulation of CQI information is determined up to QPSK. If QPSK mappingis used for an SC-FDMA symbol, a CQI value of 10 bits may be carried onone slot because a CQI value of 2 bits may be carried on the SC-FDMAsymbol. Accordingly, a CQI value having a maximum of 20 bits may becarried on one subframe. Frequency domain spread code is used to spreadCQI information in a frequency domain.

A CAZAC sequence (e.g., ZC sequence) of a length 12 may be used as thefrequency domain spread code. Control channels may be distinguished fromeach other by applying CAZAC sequences having different cyclic shiftvalues. IFFT is performed on frequency domain-spread CQI information.

12 different UEs may be subjected to orthogonal multiplexing on the samePUCCH RB by 12 cyclic shifts having the same interval. In the case of anormal CP, a DMRS sequence on the SC-FDMA symbols 1 and 5 (on an SC-FDMAsymbol 3 in the case of an extended CP) are similar to a CQI signalsequence on a frequency domain, but modulation, such as CQI information,is not applied to the DMRS sequence.

UE may be semi-statically configured by higher layer signaling so thatit periodically reports different CQI, PMI and RI Types on PUCCHresources indicated by PUCCH resource indices n_(PUCCH)^((1,{tilde over (p)})), n_(PUCCH) ^((2,{tilde over (p)})), andn_(PUCCH) ^((3,{tilde over (p)})). In this case, the PUCCH resourceindex n_(PUCCH) ^((2,{tilde over (p)})) is information indicative of aPUCCH region that is used to transmit the PUCCH format 2/2a/2b and thevalue of a Cyclic Shift (CS) to be used.

PUCCH Channel Structure

The PUCCH format 1a and 1b is described below.

In the PUCCH format 1a/1b, a symbol modulated using a BPSK or QPSKmodulation scheme is multiplied by a CAZAC sequence of a length 12. Forexample, the results of a modulation symbol d(0) by a CAZAC sequencer(n)(n=0, 1, 2, . . . , N−1) of a length N become y(0), y(1), y(2), . .. , y(N−1). The symbols y(0), . . . , y(N−1) may be called a block ofsymbols. After the modulation symbol is multiplied by the CAZACsequence, block-wise spread using an orthogonal sequence is applied.

A Hadamard sequence of a length 4 is used for common ACK/NACKinformation, and a Discrete Fourier Transform (DFT) sequence of a length3 is used for shortened ACK/NACK information and a reference signal.

In the case of an extended CP, a Hadamard sequence of a length 2 is usedin a reference signal.

FIG. 7 shows the structure of an ACK/NACK channel in the case of anormal CP in a wireless communication system to which an embodiment ofthe present invention may be applied.

FIG. 7 illustrates a PUCCH channel structure for transmitting HARQACK/NACK without a CQI.

A Reference Signal (RS) is carried on 3 contiguous SC-FDMA symbol thatbelong to 7 SC-FDMA symbols included in one slot and that are placed ina middle portion, and an ACK/NACK signal is carried on the remaining 4SC-FDMA symbols of the 7 SC-FDMA symbols.

Meanwhile, in the case of an extended CP, an RS may be carried on 2contiguous symbols placed in the middle of one slot. The number andpositions of symbols used in an RS may be different depending on controlchannels, and the number and positions of symbols used in an ACK/NACKsignal associated with the control channels may be changed depending onthe number and positions of symbols used in the RS.

ACK information (not-scrambled state) of 1 bit and 2 bits may berepresented as one HARQ ACK/NACK modulation symbol using respective BPSKand QPSK modulation schemes. Positive ACK (ACK) may be encoded as “1”,and negative ACK (NACK) may be encoded as “0”.

When a control signal is to be transmitted within an allocatedbandwidth, two-dimensional spreading is applied in order to increasemultiplexing capacity. That is, in order to increase the number of UEsor the number of control channels that may be multiplexed, frequencydomain spreading and time domain spreading are used at the same time.

In order to spread an ACK/NACK signal in a frequency domain, a frequencydomain sequence is used as a base sequence. A Zadoff-Chu (ZC) sequencewhich is one of CAZAC sequences, may be used as the frequency domainsequence. For example, by applying a different Cyclic Shift (CS) to a ZCsequence which is a base sequence, different UEs or different controlchannels may be multiplexed. The number of CS resources supported in aSC-FDMA symbol for PUCCH RBs for transmitting HARQ ACK/NACK isconfigured by a cell-specific upper layer signaling parameter shiftΔ_(shift) ^(PUCCH).

An ACK/NACK signal spread in a frequency domain is spread in a timedomain using orthogonal spreading code. A Walsh-Hadamard sequence or DFTsequence may be used as the orthogonal spreading code. For example, anACK/NACK signal may be spread for 4 symbols using an orthogonal sequencew0, w1, w2, or w3 of a length 4. Furthermore, an RS is also spread usingan orthogonal sequence of a length 3 or length 2. This is calledOrthogonal Covering (OC).

A plurality of UEs may be multiplexed using a Code Division Multiplexing(CDM) method using CS resources in a frequency domain and OC resourcesin a time domain, such as those described above. That is, ACK/NACKinformation and RSs of a large number of UEs may be multiplexed on thesame PUCCH RB.

The number of spreading code supported for ACK/NACK information isrestricted by the number of RS symbols with respect to such time domainspreading CDM. That is, the multiplexing capacity of an RS is smallerthan the multiplexing capacity of ACK/NACK information because thenumber of SC-FDMA symbols for RS transmission is smaller than the numberof SC-FDMA symbols for ACK/NACK information transmission.

For example, in the case of a normal CP, ACK/NACK information may betransmitted in 4 symbols. 3 pieces of orthogonal spreading code not 4are used for ACK/NACK information. The reason for this is that only 3pieces of orthogonal spreading code may be used for an RS because thenumber of symbols for RS transmission is limited to 3.

In case that 3 symbols of one slot may be used for RS transmission and 4symbols of the slot may be used for ACK/NACK information transmission ina subframe of a normal CP, for example, if 6 Cyclic Shifts (CSs) may beused in a frequency domain and 3 Orthogonal Cover (OC) resources may beused in a time domain, HARQ ACK from a total of 18 different UEs may bemultiplexed within one PUCCH RB. In case that 2 symbols of one slot areused for RS transmission and 4 symbols of one slot are used for ACK/NACKinformation transmission in a subframe of an extended CP, for example,if 6 CSs may be used in a frequency domain and 2 OC resources may beused in a time domain, HARQ ACK from a total of 12 different UEs may bemultiplexed within one PUCCH RB.

The PUCCH format 1 is described below. A Scheduling Request (SR) istransmitted in such a way as to make a request or does not make arequest that UE is scheduled. An SR channel reuses an ACK/NACK channelstructure in the PUCCH format 1a/1b and consists of an On-Off Keying(OKK) method based on an ACK/NACK channel design. An RS is nottransmitted in the SR channel. Accordingly, a sequence of a length 7 isused in the case of a normal CP, and a sequence of a length 6 is used inthe case of an extended CP. Different cyclic shifts or orthogonal coversmay be allocated to an SR and ACK/NACK. That is, in order to send apositive SR, UE sends HARQ ACK/NACK through a resource allocated for theSR. In order to send a negative SR, UE sends HARQ ACK/NACK through aresource allocated for ACK/NACK.

An enhanced-PUCCH (e-PUCCH) format is described below. An e-PUCCH maycorrespond to the PUCCH format 3 of an LTE-A system. A block spreadingscheme may be applied to ACK/NACK transmission using the PUCCH format 3.

Unlike in the existing PUCCH format 1 series or 2 series, the blockspreading scheme is a method of modulating control signal transmissionusing an SC-FDMA method. As shown in FIG. 8, a symbol sequence may bespread in a time domain using Orthogonal Cover Code (OCC) andtransmitted. By using OCC, the control signals of a plurality of UEs maybe multiplexed on the same RB. In the case of the PUCCH format 2, onesymbol sequence is transmitted in a time domain, and the control signalsof a plurality of UEs are multiplexed using a Cyclic Shift (CS) of aCAZAC sequence. In contrast, in the case of a block spreading-basedPUCCH format (e.g., the PUCCH format 3), one symbol sequence istransmitted in a frequency domain, and the control signals of aplurality of UEs are multiplexed using time domain spreading using OCC.

FIG. 8 shows an example in which 5 SC-FDMA symbols are generated andtransmitted during one slot in a wireless communication system to whichan embodiment of the present invention may be applied.

FIG. 8 shows an example in which 5 SC-FDMA symbols (i.e., a data part)are generated using OCC of a length=5 (or SF=5) in one symbol sequenceduring 1 slot and transmitted. In this case, 2 RS symbols may be usedduring the 1 slot.

In the example of FIG. 8, the RS symbols may be generated from a CAZACsequence to which a specific CS value has been applied and may betransmitted in a form in which a specific OCC may be applied (ormultiplied) to a plurality of RS symbols. Furthermore, in the example ofFIG. 8, assuming that 12 modulation symbols are used in each OFDM symbol(or SC-FDMA symbol) and each of the modulation symbols is generated byQPSK, a maximum number of bits capable of being transmitted in one slotare 12×2=24 bits. Accordingly, a total number of bits capable of beingtransmitted in 2 slots are 48 bits. As described above, if a PUCCHchannel structure using a block spreading method is used, controlinformation having an extended size compared to the existing PUCCHformat 1 series and 2 series can be transmitted.

General Carrier Aggregation

A communication environment taken into consideration in embodiments ofthe present invention includes a multi-carrier support environment. Thatis, a multi-carrier system or Carrier Aggregation (CA) system that isused in an embodiment of the present invention refers to a system inwhich one or more Component Carriers (CCs) having a smaller bandwidththan a target bandwidth are aggregated and used when the target widebandis configured in order to support a wideband.

In an embodiment of the present invention, a multi-carrier means of anaggregation of carriers (or a carrier aggregation). In this case, anaggregation of carriers means both an aggregation between contiguouscarriers and an aggregation between discontiguous (or non-contiguous)carriers. Furthermore, the number of CCs aggregated between downlink anduplink may be different. A case where the number of downlink CCs(hereinafter called “DL CCs”) and the number of uplink CCs (hereinaftercalled “UL CCs”) are the same is called a symmetric aggregation. A casewhere the number of DL CCs is different from the number of UL CCs iscalled an asymmetric aggregation. Such the term of a carrier aggregationmay be replaced with terms, such as a carrier aggregation, bandwidthaggregation, or spectrum aggregation.

An object of a carrier aggregation configured by aggregating two or morecomponent carriers is to support up to a 100 MHz bandwidth in an LTE-Asystem. When one or more carriers having a smaller bandwidth than atarget bandwidth are aggregated, the bandwidth of the aggregatedcarriers may be restricted to a bandwidth which is used in an existingsystem in order to maintain backward compatibility with an existing IMTsystem. For example, in an existing 3GPP LTE system, {1.4, 3, 5, 10, 15,20} MHz bandwidths may be supported. In a 3GPP LTE-advanced system(i.e., LTE-A), bandwidths greater than the bandwidth 20 MHz may besupported using only the bandwidths for a backward compatibility withexisting systems. Furthermore, in a carrier aggregation system used inan embodiment of the present invention, new bandwidths may be definedregardless of the bandwidths used in the existing systems in order tosupport a carrier aggregation.

An LTE-A system uses the concept of a cell in order to manage radioresources.

The aforementioned carrier aggregation environment may also be called amulti-cell environment. A cell is defined as a combination of a pair ofa downlink resource (DL CC) and an uplink resource (UL CC), but anuplink resource is not an essential element. Accordingly, a cell mayconsist of a downlink resource only or a downlink resource and an uplinkresource. If specific UE has a single configured serving cell, it mayhave 1 DL CC and 1 UL CC. If specific UE has two or more configuredserving cells, it has DL CCs corresponding to the number of cells, andthe number of UL CCs may be the same as or smaller than the number of DLCCs.

In some embodiments, a DL CC and an UL CC may be configured in anopposite way. That is, if specific UE has a plurality of configuredserving cells, a carrier aggregation environment in which the number ofUL CCs is greater than the number of DL CCs may also be supported. Thatis, a carrier aggregation may be understood as being an aggregation oftwo or more cells having different carrier frequency (the centerfrequency of a cell). In this case, the “cell” should be distinguishedfrom a “cell”, that is, a region commonly covered by an eNB.

A cell used in an LTE-A system includes a Primary Cell (PCell) and aSecondary Cell (SCell). A PCell and an SCell may be used as servingcells. In the case of UE which is in an RRC_CONNECTED state, but inwhich a carrier aggregation has not been configured or which does notsupport a carrier aggregation, only one serving cell configured as onlya PCell is present. In contrast, in the case of UE which is in theRRC_CONNECTED state and in which a carrier aggregation has beenconfigured, one or more serving cells may be present. A PCell and one ormore SCells are included in each serving cell.

A serving cell (PCell and SCell) may be configured through an RRCparameter. PhysCellId is the physical layer identifier of a cell and hasan integer value from 0 to 503. SCellIndex is a short identifier whichis used to identify an SCell and has an integer value of 1 to 7.ServCellIndex is a short identifier which is used to identify a servingcell (PCell or SCell) and has an integer value of 0 to 7. The value 0 isapplied to a PCell, and SCellIndex is previously assigned in order toapply it to an SCell. That is, in ServCellIndex, a cell having thesmallest cell ID (or cell index) becomes a PCell.

A PCell means a cell operating on a primary frequency (or primary CC). APCell may be used for UE to perform an initial connection establishmentprocess or a connection re-establishment process and may refer to a cellindicated in a handover process. Furthermore, a PCell means a cell thatbelongs to serving cells configured in a carrier aggregation environmentand that becomes the center of control-related communication. That is,UE may receive a PUCCH allocated only in its PCell and send the PUCCHand may use only the PCell to obtain system information or to change amonitoring procedure. An Evolved Universal Terrestrial Radio AccessNetwork (E-UTRAN) may change only a PCell for a handover procedure usingthe RRC connection reconfiguration (RRCConnectionReconfiguration)message of a higher layer including mobility control information(mobilityControllnfo) for UE which supports a carrier aggregationenvironment.

An SCell may mean a cell operating on a secondary frequency (orsecondary CC). Only one PCell is allocated to specific UE, and one ormore SCells may be allocated to the specific UE. An SCell may beconfigured after RRC connection is established and may be used toprovide additional radio resources. A PUCCH is not present in theremaining cells, that is, SCells that belong to serving cells configuredin a carrier aggregation environment and that do not include a PCell.When adding an SCell to UE supporting a carrier aggregation environment,an E-UTRAN may provide all types of system information related to theoperation of a related cell in the RRC_CONNECTED state through adedicated signal. A change of system information may be controlled byreleasing and adding a related SCell. In this case, the RRC connectionreconfiguration (RRCConnectionReconfigutaion) message of a higher layermay be used. An E-UTRAN may send dedicated signaling having a differentparameter for each UE instead of broadcasting within a related SCell.

After an initial security activation process is started, an E-UTRAN mayconfigure a network including one or more SCells by adding to a PCellthat is initially configured in a connection establishing process. In acarrier aggregation environment, a PCell and an SCell may operaterespective component carriers. In the following embodiments, a PrimaryComponent Carrier (PCC) may be used as the same meaning as a PCell, anda Secondary Component Carrier (SCC) may be used as the same meaning asan SCell.

FIG. 9 shows an example of component carriers and a carrier aggregationin a wireless communication system to which an embodiment of the presentinvention may be applied.

FIG. 9a shows the structure of a single carrier used in an LTE system. Acomponent carrier includes a DL CC and an UL CC. One component carriermay have a frequency range of 20 MHz.

FIG. 9b shows the structure of a carrier aggregation used in an LTE-Asystem. FIG. 9b shows an example in which 3 component carriers eachhaving a frequency size of 20 MHz have been aggregated. Three DL CCs andthree UL CCs have been illustrated in FIG. 9, but the number of DL CCsand UL CCs is not limited. In the case of a carrier aggregation, UE maymonitor 3 CCs at the same time, may receive downlink signal/data, andmay transmit uplink signal/data.

If N DL CCs are managed in a specific cell, a network may allocate M(M≦N) DL CCs to UE. In this case, the UE may monitor only the M limitedDL CCs and receive a DL signal. Furthermore, a network may give priorityto L (L≦M≦N) DL CCs and allocate major DL CCs to UE. In this case, theUE must monitor the L DL CCs. Such a method may be applied to uplinktransmission in the same manner.

A linkage between a carrier frequency (or DL CC) of a downlink resourceand a carrier frequency (or UL CC) of an uplink resource may beindicated by a higher layer message, such as an RRC message, or systeminformation. For example, a combination of DL resources and UL resourcesmay be configured by a linkage defined by System Information Block Type2(SIB2). Specifically, the linkage may mean a mapping relationshipbetween a DL CC in which a PDCCH carrying an UL grant is transmitted andan UL CC in which the UL grant is used and may mean a mappingrelationship between a DL CC (or UL CC) in which data for an HARQ istransmitted and an UL CC (or DL CC) in which an HARQ ACK/NACK signal istransmitted.

Cross-Carrier Scheduling

In a carrier aggregation system, there are two methods, that is, aself-scheduling method and a cross-carrier scheduling method form thepoint of view of scheduling for a carrier or a serving cell.Cross-carrier scheduling may also be called cross-component carrierscheduling or cross-cell scheduling.

Cross-carrier scheduling means that a PDCCH (DL grant) and a PDSCH aretransmitted in different DL CCs or that a PUSCH transmitted according toa PDCCH (UL grant) transmitted in a DL CC is transmitted through an ULCC different from an UL CC that is linked to the DL CC through which theUL grant has been received.

Whether cross-carrier scheduling will be performed may be activated ordeactivate in a UE-specific way, and each UE may be notified throughhigh layer signaling (e.g., RRC signaling) semi-statically.

If cross-carrier scheduling is activated, there is a need for a CarrierIndicator Field (CIF) providing notification that a PDSCH/PUSCHindicated by a PDCCH is transmitted through which DL/UL CC. For example,a PDCCH may allocate a PDSCH resource or PUSCH resource to any one of aplurality of component carriers using a CIF. That is, if a PDCCH on a DLCC allocates a PDSCH or PUSCH resource to one of multi-aggregated DL/ULCCs, a CIF is configured. In this case, a DCI format of LTE-A Release-8may be extended according to the CIF. In this case, the configured CIFmay be fixed to a 3-bit field, and the position of the configured CIFmay be fixed regardless of the size of the DCI format. Furthermore, aPDCCH structure (resource mapping based on the same coding and the sameCCE) of LTE-A Release-8 may be reused.

In contrast, if a PDCCH on a DL CC allocates a PDSCH resource on thesame DL CC or allocates a PUSCH resource on a single-linked UL CC, a CIFis not configured. In this case, the same PDCCH structure (resourcemapping based on the same coding and the same CCE) and DCI format asthose of LTE-A Release-8 may be used.

If cross-carrier scheduling is possible, UE needs to monitor a PDCCH fora plurality of pieces of DCI in the control region of a monitoring CCbased on a transmission mode and/or bandwidth corresponding to each CC.Accordingly, there is a need for the configuration of a search space andPDCCH monitoring capable of supporting such monitoring.

In a carrier aggregation system, a UE DL CC set is indicative of a setof DL CCs scheduled so that UE receives a PDSCH. A UE UL CC set isindicative of a set of UL CCs scheduled so that UE transmits a PUSCH.Furthermore, a PDCCH monitoring set is indicative of a set of one ormore DL CCs for performing PDCCH monitoring. A PDCCH monitoring set maybe the same as a UE DL CC set or may be a subset of a UE DL CC set. APDCCH monitoring set may include at least one of DL CCs within a UE DLCC set. Alternatively, a PDCCH monitoring set may be separately definedregardless of a UE DL CC set. DL CCs included in a PDCCH monitoring setmay be configured so that self-scheduling for a linked UL CC is alwayspossible. Such a UE DL CC set, UE UL CC set, and PDCCH monitoring setmay be configured in a UE-specific, UE group-specific, or cell-specificway.

If cross-carrier scheduling is deactivated, it means that a PDCCHmonitoring set is always the same as UE DL CC set. In this case, thereis no indication, such as separate signaling for a PDCCH monitoring set.However, if cross-carrier scheduling is activated, a PDCCH monitoringset may be defined in a UE DL CC set. That is, in order to schedule aPDSCH or PUSCH for UE, an eNB transmits a PDCCH through a PDCCHmonitoring set only.

FIG. 10 shows an example of the structure of a subframe according tocross-carrier scheduling in a wireless communication system to which anembodiment of the present invention may be applied.

FIG. 10 shows an example in which 3 DL CCs are aggregated in a DLsubframe for LTE-A UE and a DL CC “A” has been configured as a PDCCHmonitoring DL CC. IF a CIF is not used, each DL CC may send a PDCCH forscheduling its PDSCH without a CIF. In contrast, if a CIF is usedthrough higher layer signaling, only the single DL CC “A” may send itsPDSCH or a PDCCH for scheduling a PDSCH of a different CC using the CIF.In this case, the DL CCs “B” and “C” not configured as PDCCH monitoringDL CCs do not send a PDCCH.

General ACK/NACK Multiplexing Method

In a situation in which UE has to simultaneously send a plurality ofACK/NACKs corresponding to a plurality of data units received from aneNB, an ACK/NACK multiplexing method based on the selection of a PUCCHresource may be taken into consideration in order to maintain the singlefrequency characteristic of an ACK/NACK signal and to reduce ACK/NACKtransmission power.

The content of ACK/NACK responses for a plurality of data units,together with ACK/NACK multiplexing, is identified by a combination of aPUCCH resource used in actual ACK/NACK transmission and the resource ofQPSK modulation symbols.

For example, if one PUCCH resource sends 4 bits and a maximum of 4 dataunits are transmitted, ACK/NACK results may be identified in an eNB asin Table 3 below.

TABLE 3 HARQ-ACK (0), HARQ-ACK (1), b (0), HARQ-ACK (2), HARQ-ACK (3)n_(PUCCH) ⁽¹⁾ b (1) ACK, ACK, ACK, ACK n_(PUCCH, 1) ⁽¹⁾ 1, 1 ACK, ACK,ACK, NACK/DTX n_(PUCCH, 1) ⁽¹⁾ 1, 0 NACK/DTX, NACK/DTX, NACK, DTXn_(PUCCH, 2) ⁽¹⁾ 1, 1 ACK, ACK, NACK/DTX, ACK n_(PUCCH, 1) ⁽¹⁾ 1, 0NACK, DTX, DTX, DTX n_(PUCCH, 0) ⁽¹⁾ 1, 0 ACK, ACK, NACK/DTX, NACK/DTXn_(PUCCH, 1) ⁽¹⁾ 1, 0 ACK, NACK/DTX, ACK, ACK n_(PUCCH, 3) ⁽¹⁾ 0, 1NACK/DTX, NACK/DTX, NACK/DTX, NACK n_(PUCCH, 3) ⁽¹⁾ 1, 1 ACK, NACK/DTX,ACK, NACK/DTX n_(PUCCH, 2) ⁽¹⁾ 0, 1 ACK, NACK/DTX, NACK/DTX, ACKn_(PUCCH, 0) ⁽¹⁾ 0, 1 ACK, NACK/DTX, NACK/DTX, NACK/DTX n_(PUCCH, 0) ⁽¹⁾1, 1 NACK/DTX, ACK, ACK, ACK n_(PUCCH, 3) ⁽¹⁾ 0, 1 NACK/DTX, NACK, DTX,DTX n_(PUCCH, 1) ⁽¹⁾ 0, 0 NACK/DTX, ACK, ACK, NACK/DTX n_(PUCCH, 2) ⁽¹⁾1, 0 NACK/DTX, ACK, NACK/DTX, ACK n_(PUCCH, 3) ⁽¹⁾ 1, 0 NACK/DTX, ACK,NACK/DTX, NACK/DTX n_(PUCCH, 1) ⁽¹⁾ 0, 1 NACK/DTX, NACK/DTX, ACK, ACKn_(PUCCH, 3) ⁽¹⁾ 0, 1 NACK/DTX, NACK/DTX, ACK, NACK/DTX n_(PUCCH, 2) ⁽¹⁾0, 0 NACK/DTX, NACK/DTX, NACK/DTX, ACK n_(PUCCH, 3) ⁽¹⁾ 0, 0 DTX, DTX,DTX, DTX N/A N/A

In Table 3, HARQ-ACK (i) is indicative of ACK/NACK results for an i-thdata unit. In Table 3, discontinuous transmission (DTX) means that thereis no data unit transmitted for a corresponding HARQ-ACK(i) or that UEdoes not detect a data unit corresponding to the HARQ-ACK(i).

In accordance with Table 3, a maximum of 4 PUCCH resources n_(PUCCH,0)⁽¹⁾, n_(PUCCH,1) ⁽¹⁾, n_(PUCCH,2) ⁽¹⁾, and n_(PUCCH,3) ⁽¹⁾ are present,and b(0), b(1) has 2 bits transmitted using a selected PUCCH.

For example, if UE successfully receives all of the 4 data units, the UEsends 2 bits (1, 1) using the PUCCH resource n_(PUCCH,) ⁽¹⁾.

If UE fails in decoding in first and third data units and succeed indecoding in second and fourth data units, the UE sends bits (1, 0) usingthe PUCCH resource n_(PUCCH,3) ⁽¹⁾.

In the selection of an ACK/NACK channel, if at least one ACK is present,NACK and DTX are coupled. The reason for this is that all of ACK/NACKstates are unable to be represented using a combination of a reservedPUCCH resource and a QPSK symbol. If ACK is not present, however, DTX isdecoupled from NACK.

In this case, a PUCCH resource linked to a data unit corresponding toone clear NACK may be reserved in order to send a signal for a pluralityof ACKs/NACKs.

PDCCH Validation for Semi-Persistent Scheduling

Semi-Persistent Scheduling (SPS) is a scheduling method for allocatingresources to specific UE so that the resources continue to be maintainedduring a specific time interval.

If a specific amount of data is transmitted during a specific time as ina Voice over Internet Protocol (VoIP), the waste of control informationcan be reduced using the SPS method because the control information doesnot need to be transmitted at each data transmission interval forresource allocation. In a so-called SPS method, a time resource area inwhich resources may be allocated is first allocated to UE.

In this case, in the semi-persistent allocation method, a time resourcearea allocated to specific UE may be configured to have a cycle. Next,the allocation of time-frequency resources is completed by allocating afrequency resource area, if necessary. The allocation of a frequencyresource area as described above may be called so-called activation. Ifthe semi-persistent allocation method is used, resource allocation ismaintained by one signaling during a specific period. Accordingly,signaling overhead can be reduced because resource allocation does notneed to be repeatedly performed.

Thereafter, if resource allocation for the UE is not required, signalingfor releasing the frequency resource allocation may be transmitted froman eNB to the UE. The release of the allocation of a frequency resourcearea as described above may be called deactivation.

In current LTE, for SPS for uplink and/or downlink, first, UE isnotified of that SPS transmission/reception need to be performed in whatsubframes through Radio Resource Control (RRC) signaling. That is, atime resource of time-frequency resources allocated for SPS is firstdesignated through RRC signaling. In order to notify the UE of availablesubframes, for example, the UE may be notified of the cycle and offsetof a subframe. However, the UE does not immediately performtransmission/reception according to SPS although it has received RRCsignaling because only the time resource area is allocated to the UEthrough RRC signaling. The allocation of the time-frequency resources iscompleted by allocating a frequency resource area, if necessary. Theallocation of a frequency resource area as described above may be calledactivation, and the release of the allocation of a frequency resourcearea may be called deactivation.

Accordingly, the UE receives a PDCCH indicative of activation, allocatesa frequency resource based on RB allocation information included in thereceived PDCCH, and starts to perform transmission/reception based on asubframe cycle and offset allocated through RRC signaling by applying amodulation scheme and coding rate according to Modulation and CodingScheme (MCS) information.

Next, when receiving a PDCCH indicative of deactivation from an eNB, theUE stops the transmission/reception. When a PDCCH indicative ofactivation or reactivation is received after the transmission/receptionis stopped, the UE resumes transmission/reception using a subframe cycleand offset allocated through RRC signaling using RBs and an MCSdesignated in the corresponding PDCCH. That is, the allocation of timeresources is performed through RRC signaling, but thetransmission/reception of actual signals may be performed after a PDCCHindicative of the activation and reactivation of SPS is received. Thestop of signal transmission/reception is performed after a PDCCHindicative of the deactivation of SPS is received.

If the following conditions are all satisfied, the UE may validate aPDCCH including an SPS indication. First, CRC parity bits added forPDCCH payload need to be scrambled with an SPS C-RNTI. Second, a NewData Indicator (NDI) field needs to be set to 0. In this case, in thecase of the DCI formats 2, 2A, 2B, and 2C, an NDI field is indicative ofone of activated transport blocks.

Furthermore, the validation of each field used in the DCI format iscompleted when each field is set based on Table 4 and Table 5 below.When such a validation is completed, the UE recognizes the received DCIinformation as being valid SPS activation or deactivation (or release).In contrast, if the validation is not completed, the UE recognizes thatnon-matching CRC is included in a received DCI format.

Table 4 illustrates fields for PDCCH validation indicative of SPSactivation.

TABLE 4 DCI DCI DCI FORMAT FORMAT FORMAT 0 1/1A 2/2A/2B TPC command forset to N/A N/A scheduled PUSCH “00” Cyclic shift DMRS set to N/A N/A“000” MCS and redundancy MSB is N/A N/A version set to “0” HARQ processN/A FDD: set FDD: set to number to “000” “000” TDD: set TDD: set to to“0000” “0000” MCS N/A MSB is set For an enabled to “0” transport block:MSB is set to “0” Redundancy version N/A set to For the enabled “00”transport block: set to “00”

Table 5 illustrates fields for PDCCH validation indicative of SPSdeactivation (or release).

TABLE 5 DCI DCI format format 0 1A TPC command for set to N/A scheduledPUSCH “00” Cyclic shift DMRS set to N/A “000” MCS and redundancy set toN/A version “11111” Resource block Set to N/A assignment and all “1”shopping resource allocation HARQ process N/A FDD: set number to “000”TDD: set to “0000” MCS N/A set to “11111” Redundancy version N/A set to“00” Resource block N/A Set to assignment all “1”s

If a DCI format is indicative of SPS downlink scheduling activation, aTPC command value for a PUCCH field may be used an index indicative of 4PUCCH resource values set by a higher layer.

PUCCH Piggybacking in Rel-8 LTE

FIG. 11 shows an example of transport channel processing for an UL-SCHin a wireless communication system to which an embodiment of the presentinvention may be applied.

In a 3GPP LTE system (=E-UTRA, Rel. 8), in the case of UL, in order toefficiently use the power amplifier of UE, a Peak-to-Average Power Ratio(PAPR) characteristic or Cubic Metric (CM) characteristic affectingperformance of the power amplifier are set to maintain good singlecarrier transmission. That is, in the case of PUSCH transmission in anexisting LTE system, the single carrier characteristic of data may bemaintained through DFT-precoding. In the case of PUCCH transmission, asingle carrier characteristic may be maintained by carrying informationon a sequence having a single carrier characteristic and sending theinformation. However, if DFT-precoded data is discontiguously allocatedbased on a frequency axis, or a PUSCH and a PUCCH are transmitted at thesame time, such a single carrier characteristic is not maintained.Accordingly, if PUSCH transmission is to be performed in the samesubframe as that of PUCCH transmission as in FIG. 11, Uplink ControlInformation (UCI) information to be transmitted through a PUCCH istransmitted (piggybacked) along with data through a PUSCH in order tomaintain the single carrier characteristic.

In a subframe in which a PUSCH is transmitted, a method of multiplexingUplink Control Information (UCI) (a CQI/PMI, HARQ-ACK, an RI, etc.) witha PUSCH region is used because existing LTE UE is unable to send a PUCCHand a PUSCH at the same time as described above.

For example, if a Channel Quality Indicator (CQI) and/or a PrecodingMatrix Indicator (PMI) are to be transmitted in a subframe allocated tosend a PUSCH, UL-SCH data and the CQI/PMI may be multiplexed prior toDFT-spreading and may be transmitted along with control information anddata. In this case, the UL-SCH data is subjected to rate matching bytaking the CQI/PMI resources into consideration. Furthermore, a methodof puncturing the UL-SCH data into control information, such as HARQACK, and an RI, and multiplexing the results with a PUSCH region isused.

FIG. 12 shows an example of a signal processing process in an uplinkshared channel, that is, a transport channel, in a wirelesscommunication system to which an embodiment of the present invention maybe applied.

Hereinafter, a signal processing process for an uplink shared channel(hereinafter called an “UL-SCH”) may be applied to one or more transportchannels or control information types.

Referring to FIG. 12, an UL-SCH transfers data to a coding unit in theform of a Transport Block (TB) once for each Transmission Time Interval(TTI).

CRC parity bits p₀, p₁, p₂, p₃, . . . , P_(L-1) are attached to the bitsa₀, a₁, a₂, a₃, . . . , a_(A-1) of bits the transport block receivedfrom a higher layer at step S120. In this case, A is the size of thetransport block, and L is the number of parity bits. The input bits towhich the CRC parity bits have been attached are b₀, b₁, b₂, b₃, . . . ,b_(B-1). In this case, B is indicative of the number of bits of thetransport block including the CRC parity bits.

The input bits b₀, b₁, b₂, b₃, . . . , b_(B-1) are segmented intoseveral Code Blocks (CBs) based on the TB size. A CRC is attached to thesegmented several CBs at step S121. Bits after the segmentation of theCBs and the attachment of the CRC are c_(r0), c_(r1), c_(r2), c_(r3), .. . , C_(r(K) _(r) ⁻¹⁾. In this case, r is a CB number (r=0, . . . ,C−1), and K_(r) is the number of bits according to a CB r. Furthermore,C is a total number of CBs.

Next, channel coding is performed at step S122. Output bits after thechannel coding are d_(r0) ^((i)), d_(r1) ^((i)), d_(r2) ^((i)), d_(r3)^((i)), . . . d_(r(D) _(r) ⁻¹⁾ ^((i)). In this case, i is a coded streamindex and may have a value 0, 1, or 2 value. D_(r) is the number of bitsof the i-th-coded stream for the CB r. r is a CB number (r=0, . . . ,C−1), and C a total number of CBs. Each CB may be coded by turbo coding.

Next, rate matching is performed at step S123. Bits after the ratematching are e_(r0), e_(r1), e_(r2), e_(r3), . . . , e_(r(E) _(r) ⁻¹⁾.In this case, r is a CB number (r=0, . . . , C−1), and C is a totalnumber of CBs. E_(r) is the number of bits of a r-th code block that hasbeen subjected to rate matching.

Next, a concatenation between the CBs is performed again at step S124.Bits after the concatenation of the CBs are f₀, f₁, f₂, f₃, . . . ,f_(G-1). In this case, G is a total number of coded bits fortransmission. When control information is multiplexed with UL-SCHtransmission, the number of bits used for control informationtransmission is not included.

Meanwhile, when control information is transmitted in a PUSCH, channelcoding is independently performed on a CQI/PMI, an RI, and ACK/NACK,that is, the control information, at steps S126, S127, and S128. Thepieces of control information have different coding rates becausedifferent coded symbols are allocated for the transmission of thecontrol information.

In Time Division Duplex (TDD), ACK/NACK feedback mode supports two typesof ACK/NACK bundling mode and ACK/NACK multiplexing mode by theconfiguration of a higher layer. For ACK/NACK bundling, ACK/NACKinformation bits include 1 bit or 2 bits. For ACK/NACK multiplexing,ACK/NACK information bits include 1 bit to 4 bits.

After the concatenation between the CBs at step S124, the multiplexingof the coded bits f₀, f₁, f₂, f₃, . . . , f_(G-1) of the UL-SCH data andthe coded bits q₀, q₁, q₂, q₃, . . . , q_(N) _(L) _(·Q) _(CQI) ⁻¹ of theCQI/PMI are performed at step S125. The results of the multiplexing ofthe UL-SCH data and the CQI/PMI are g ₀, g ₁, g ₂, g ₃, . . . , g_(H′-1). In this case, (i=0, . . . , H′−1) is indicative of a columnvector having a length (Q_(m)·N_(L)). H=(G+N_(L)·Q_(CQI)) andH′=H/(N_(L)·Q_(m)). N_(L) is the number of layers to which an UL-SCHtransport block has been mapped. H is a total number of coded bitsallocated to the N_(L) transmission layers to which the transport blockhas been mapped for the UL-SCH data and CQI/PMI information.

Next, the multiplexed data and CQI/PMI and the separately channel-codedRI and ACK/NACK are subjected to channel interleaving, therebygenerating an output signal at step S129.

Multi-Input Multi-Output (MIMO)

A MIMO technology does not use single transmission antenna and singlereception antenna that have been commonly used so far, but uses amulti-transmission (Tx) antenna and a multi-reception (Rx) antenna. Inother words, the MIMO technology is a technology for increasing acapacity or enhancing performance using multi-input/output antennas inthe transmission end or reception end of a wireless communicationsystem. Hereinafter, MIMO is called a “multi-input/output antenna.”.

More specifically, the multi-input/output antenna technology does notdepend on a single antenna path in order to receive a single totalmessage and completes total data by collecting a plurality of datapieces received through several antennas. As a result, themulti-input/output antenna technology can increase a data transfer ratewithin a specific system range and can also increase a system rangethrough a specific data transfer rate.

It is expected that an efficient multi-input/output antenna technologywill be used because next-generation mobile communication requires adata transfer rate much higher than that of existing mobilecommunication. In such a situation, the MIMO communication technology isa next-generation mobile communication technology which may be widelyused in mobile communication UE and a relay node and has been in thespotlight as a technology which may overcome a limit to the transferrate of another mobile communication attributable to the expansion ofdata communication.

Meanwhile, the multi-input/output antenna (MIMO) technology of varioustransmission efficiency improvement technologies that are beingdeveloped has been most in the spotlight as a method capable ofsignificantly improving a communication capacity andtransmission/reception performance even without the allocation ofadditional frequencies or a power increase.

FIG. 13 shows the configuration of a known MIMO communication system.

Referring to FIG. 13, if the number of transmission (Tx) antennas isincreased to N_(T) and the number of reception (Rx) antennas isincreased to N_(R) at the same time, a theoretical channel transmissioncapacity is increased in proportion to the number of antennas, unlike inthe case where a plurality of antennas is used only in a transmitter ora receiver. Accordingly, a transfer rate can be improved, and frequencyefficiency can be significantly improved. In this case, a transfer rateaccording to an increase of a channel transmission capacity may betheoretically increased by a value obtained by multiplying the followingrate increment R_(i) by a maximum transfer rate R_(o) if one antenna isused.

R=min(N _(T) ,N _(R))  [Equation 1]

That is, in an MIMO communication system using 4 transmission antennasand 4 reception antennas, for example, a quadruple transfer rate can beobtained theoretically compared to a single antenna system.

Such a multi-input/output antenna technology may be divided into aspatial diversity method for increasing transmission reliability usingsymbols passing through various channel paths and a spatial multiplexingmethod for improving a transfer rate by sending a plurality of datasymbols at the same time using a plurality of transmission antennas.Furthermore, active research is being recently carried out on a methodfor properly obtaining the advantages of the two methods by combiningthe two methods.

Each of the methods is described in more detail below. First, thespatial diversity method includes a space-time block code-series methodand a space-time Trelis code-series method using a diversity gain and acoding gain at the same time. In general, the Trelis code-series methodis better in terms of bit error rate improvement performance and thedegree of a code generation freedom, whereas the space-time blockcode-series method has low operational complexity. Such a spatialdiversity gain may correspond to an amount corresponding to the product(NT×NR) of the number of transmission antennas (NT) and the number ofreception antennas (NR).

Second, the spatial multiplexing scheme is a method for sendingdifferent data streams in transmission antennas. In this case, in areceiver, mutual interference is generated between data transmitted by atransmitter at the same time. The receiver removes the interferenceusing a proper signal processing scheme and receives the data. A noiseremoval method used in this case may include a Maximum LikelihoodDetection (MLD) receiver, a Zero-Forcing (ZF) receiver, a Minimum MeanSquare Error (MMSE) receiver, Diagonal-Bell Laboratories LayeredSpace-Time (D-BLAST), and Vertical-Bell Laboratories Layered Space-Time(V-BLAST). In particular, if a transmission end can be aware of channelinformation, a Singular Value Decomposition (SVD) method may be used.

Third, there is a method using a combination of a spatial diversity andspatial multiplexing. If only a spatial diversity gain is to beobtained, a performance improvement gain according to an increase of adiversity disparity is gradually saturated. If only a spatialmultiplexing gain is used, transmission reliability in a radio channelis deteriorated. Methods for solving the problems and obtaining the twogains have been researched and may include a double space-time transmitdiversity (double-STTD) method and a space-time bit interleaved codedmodulation (STBICM).

In order to describe a communication method in a multi-input/outputantenna system, such as that described above, in more detail, thecommunication method may be represented as follows through mathematicalmodeling.

First, as shown in FIG. 13, it is assumed that N_(T) transmissionantennas and N_(R) reception antennas are present.

First, a transmission signal is described below. If the N_(T)transmission antennas are present as described above, a maximum numberof pieces of information which can be transmitted are N_(T), which maybe represented using the following vector.

s=[s ₁ ,s ₂ , . . . ,s _(N) _(T) ]^(T)  [Equation 2]

Meanwhile, transmission power may be different in each of pieces oftransmission information s₁, s₂, . . . , s_(NT). In this case, if piecesof transmission power are P₁, P₂, . . . , P_(NT), transmissioninformation having controlled transmission power may be representedusing the following vector.

ŝ=[ŝ ₁ ,ŝ ₂ , . . . ,ŝ _(N) _(T) ]^(T) =[P ₁ s ₁ ,P ₂ s ₂ , . . . ,P_(N) _(T) s _(N) _(T) ]^(T)  [Equation 3]

Furthermore, ŝ may be represented as follows using the diagonal matrix Pof transmission power.

$\begin{matrix}{\hat{s} = {{\begin{bmatrix}P_{1} & \; & \; & 0 \\\; & P_{2} & \; & \; \\\; & \; & \ddots & \; \\0 & \; & \; & P_{N_{T}}\end{bmatrix}\begin{bmatrix}s_{1} \\s_{2} \\\vdots \\s_{N_{T}}\end{bmatrix}} = {Ps}}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

Meanwhile, the information vector ŝ having controlled transmission poweris multiplied by a weight matrix W, thus forming N_(T) transmissionsignals x₁, x₂, . . . , x_(NT) that are actually transmitted. In thiscase, the weight matrix functions to properly distribute thetransmission information to antennas according to a transport channelcondition. The following may be represented using the transmissionsignals x₁, x₂, . . . , X_(NT).

$\begin{matrix}{x = {\left\lbrack \begin{matrix}x_{1} \\x_{2} \\\vdots \\x_{i} \\\vdots \\x_{N_{T}}\end{matrix} \right\rbrack = {{\begin{bmatrix}w_{11} & w_{12} & \ldots & w_{1N_{T}} \\w_{21} & w_{22} & \ldots & w_{2N_{T}} \\\vdots & \; & \ddots & \; \\w_{i\; 1} & w_{i\; 2} & \ldots & w_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\w_{N_{T}1} & w_{N_{T}2} & \ldots & w_{N_{T}N_{T}}\end{bmatrix}\begin{bmatrix}{\hat{s}}_{1} \\{\hat{s}}_{2} \\\vdots \\{\hat{s}}_{j} \\\vdots \\{\hat{s}}_{N_{T}}\end{bmatrix}} = {{W\hat{s}} = {WPs}}}}} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack\end{matrix}$

In this case, w_(ij) denotes weight between an i-th transmission antennaand a j-th transmission information, and W is an expression of a matrixof the weight. Such a matrix W is called a weight matrix or precodingmatrix.

Meanwhile, the transmission signal x, such as that described above, maybe considered to be used in a case where a spatial diversity is used anda case where spatial multiplexing is used.

If spatial multiplexing is used, all the elements of the informationvector s have different values because different signals are multiplexedand transmitted. In contrast, if the spatial diversity is used, all theelements of the information vector s have the same value because thesame signals are transmitted through several channel paths.

A method of mixing spatial multiplexing and the spatial diversity may betaken into consideration. In other words, the same signals may betransmitted using the spatial diversity through 3 transmission antennas,for example, and the remaining different signals may be spatiallymultiplexed and transmitted.

If N_(R) reception antennas are present, the reception signals y₁, y₂, .. . , y_(NR) of the respective antennas are represented as follows usinga vector y.

y=[y ₁ ,y ₂ , . . . ,y _(N) _(R) ]^(T)  [Equation 6]

Meanwhile, if channels in a multi-input/output antenna communicationsystem are modeled, the channels may be classified according totransmission/reception antenna indices. A channel passing through areception antenna i from a transmission antenna j is represented ash_(ij). In this case, it is to be noted that in order of the index ofh_(ij), the index of a reception antenna comes first and the index of atransmission antenna then comes.

Several channels may be grouped and expressed in a vector and matrixform. For example, a vector expression is described below.

FIG. 14 is a diagram showing a channel from a plurality of transmissionantennas to a single reception antenna.

As shown in FIG. 14, a channel from a total of N_(T) transmissionantennas to a reception antenna i may be represented as follows.

h _(i) ^(T) =[h _(i1) ,h _(i2) , . . . ,h _(iN) _(T) ]  [Equation 7]

Furthermore, if all channels from the N_(T) transmission antenna toN_(R) reception antennas are represented through a matrix expression,such as Equation 7, they may be represented as follows.

$\begin{matrix}{H = {\left\lbrack \begin{matrix}h_{1}^{T} \\h_{2}^{T} \\\vdots \\h_{i}^{T} \\\vdots \\h_{N_{R}}^{T}\end{matrix} \right\rbrack = \begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1N_{T}} \\h_{21} & h_{22} & \ldots & h_{2N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i\; 2} & \ldots & h_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}}} & \left\lbrack {{Equation}\mspace{14mu} 8} \right\rbrack\end{matrix}$

Meanwhile, Additive White Gaussian Noise (AWGN) is added to an actualchannel after the actual channel experiences the channel matrix H.Accordingly, AWGN n₁, n₂, . . . , n_(NR) added to the N_(R) receptionantennas, respectively, are represented using a vector as follows.

n=[n ₁ ,n ₂ , . . . ,n _(N) _(R) ]^(T)  [Equation 9]

A transmission signal, a reception signal, a channel, and AWGN in amulti-input/output antenna communication system may be represented tohave the following relationship through the modeling of the transmissionsignal, reception signal, channel, and AWGN, such as those describedabove.

$\begin{matrix}{y = {\begin{bmatrix}y_{1} \\y_{2} \\\vdots \\y_{i} \\\vdots \\y_{N_{R}}\end{bmatrix} = {{{\begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1N_{T}} \\h_{21} & h_{22} & \ldots & h_{2N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i\; 2} & \ldots & h_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}\left\lbrack \begin{matrix}x_{1} \\x_{2} \\\vdots \\x_{j} \\\vdots \\x_{N_{T}}\end{matrix} \right\rbrack} + \begin{bmatrix}n_{1} \\n_{2} \\\vdots \\n_{i} \\\vdots \\n_{N_{R}}\end{bmatrix}} = {{Hx} + n}}}} & \left\lbrack {{Equation}\mspace{14mu} 10} \right\rbrack\end{matrix}$

Meanwhile, the number of rows and columns of the channel matrix Hindicative of the state of channels is determined by the number oftransmission/reception antennas. In the channel matrix H, as describedabove, the number of rows becomes equal to the number of receptionantennas N_(R), and the number of columns becomes equal to the number oftransmission antennas N_(T). That is, the channel matrix H becomes anN_(R)×N_(T) matrix.

In general, the rank of a matrix is defined as a minimum number of thenumber of independent rows or columns. Accordingly, the rank of thematrix is not greater than the number of rows or columns. As for figuralstyle, for example, the rank H of the channel matrix H is limited asfollows.

rank(H)≦min(N _(T) ,N _(R))  [Equation 11]

Furthermore, if a matrix is subjected to Eigen value decomposition, arank may be defined as the number of Eigen values that belong to Eigenvalues and that are not 0. Likewise, if a rank is subjected to SingularValue Decomposition (SVD), it may be defined as the number of singularvalues other than 0. Accordingly, the physical meaning of a rank in achannel matrix may be said to be a maximum number on which differentinformation may be transmitted in a given channel.

In this specification, a “rank” for MIMO transmission indicates thenumber of paths through which signals may be independently transmittedat a specific point of time and a specific frequency resource. The“number of layers” indicates the number of signal streams transmittedthrough each path. In general, a rank has the same meaning as the numberof layers unless otherwise described because a transmission end sendsthe number of layers corresponding to the number of ranks used in signaltransmission.

Reference Signal (RS)

In a wireless communication system, a signal may be distorted duringtransmission because data is transmitted through a radio channel. Inorder for a reception end to accurately receive a distorted signal, thedistortion of a received signal needs to be corrected using channelinformation. In order to detect channel information, a method ofdetecting channel information using the degree of the distortion of asignal transmission when signal is transmitted through a channel and amethod of transmitting signal known to both the transmission side andthe reception side is mostly used. The aforementioned signal is called apilot signal or Reference Signal (RS).

When data is transmitted/received using a multi-input/output antenna, achannel state between a transmission antenna and a reception antennaneeds to be detected in order to accurately receive a signal.Accordingly, each transmission antenna needs to have an individualreference signal.

A downlink reference signal includes a Common Reference Signal (CRS)shared by all UEs within one cell and a Dedicated Reference Signal (DRS)for specific UE. Information for demodulation and channel measurementmay be provided using such reference signals.

The reception side (i.e., UE) measures a channel state based on a CRSand feeds indicators related to channel quality, such as a ChannelQuality Indicator (CQI), a Precoding Matrix Index (PMI) and/or a RankIndicator (RI), back to the transmission side (i.e., an eNB). The CRS isalso called a cell-specific RS. In contrast, a reference signal relatedto the feedback of Channel State Information (CSI) may be defined as aCSI-RS.

The DRS may be transmitted through resource elements if data on a PDSCHneeds to be demodulated. UE may receive information about whether a DRSis present through a higher layer, and the DRS is valid only if acorresponding PDSCH has been mapped. The DRS may also be called aUE-specific RS or demodulation RS (DMRS).

FIG. 15 illustrates a reference signal pattern mapped to a downlinkresource block pair in a wireless communication system to which anembodiment of the present invention may be applied.

Referring to FIG. 15, a downlink resource block pair, that is, a unit inwhich a reference signal is mapped unit, may be represented in the formof one subframe in a time domain X 12 subcarriers in a frequency domain.That is, in a time axis (i.e., x axis), one resource block pair has alength of 14 OFDM symbols in the case of a normal Cyclic Prefix (CP)(FIG. 15a ) and has a length of 12 OFDM symbols in the case of anextended CP (FIG. 15b ). In the resource block lattice, ResourceElements (REs) indicated by “0”, “1”, “2”, and “3” mean the positions ofthe CRSs of antenna port indices “0”, “1”, “2”, and “3”, and REsindicated by “D” denotes the position of a DRS.

A CRS is described in detail below. The CRS is used to estimate thechannel of a physical antenna and is a reference signal which may bereceived by all UEs located in a cell in common. The CRS is distributedto the entire frequency bandwidth. Furthermore, the CRS may be used forChannel Quality Information (CQI) and data demodulation.

The CRS is defined in various formats depending on an antenna array onthe transmission side (i.e., an eNB). In a 3GPP LTE system (e.g.,release-8), various antenna arrays are supported, and the transmissionside of a downlink signal has three types of antenna arrays, such as 3single transmission antennas, 2 transmission antennas, and 4transmission antennas. If an eNB uses a single transmission antenna,reference signals for a single antenna port are arrayed. If an eNB uses2 transmission antennas, reference signals for 2 transmission antennaports are arrayed using a Time Division Multiplexing (TDM) method and/ora Frequency Division Multiplexing (FDM) method. That is, different timeresources and/or different frequency resources are allocated so thatreference signals for 2 antenna ports are distinguished from each other.

Furthermore, if an eNB uses 4 transmission antennas, reference signalsfor 4 transmission antenna ports are arrayed using the TDM and/or FDMmethods. Channel information measured by the reception side (i.e., UE)of a downlink signal may be used to demodulate data transmitted using atransmission method, such as single transmission antenna transmission,transmission diversity, closed-loop spatial multiplexing, open-loopspatial multiplexing, or an multi-User-multi-input/output (MIMO)antennas.

If a multi-input/output antenna is supported, when a reference signal istransmitted by a specific antenna port, the reference signal istransmitted in the positions of resource elements specified depending onthe pattern of the reference signal and is not transmitted in thepositions of resource elements specified for other antenna ports. Thatis, reference signals between different antennas do not overlap.

A rule for mapping a CRS to a resource block is defined as follows.

$\begin{matrix}{{k = {{6m} + {\left( {v + v_{shift}} \right){mod}\; 6}}}{l = \left\{ {{{\begin{matrix}{0,{N_{symb}^{DL} - 3}} & {{{if}\mspace{14mu} p} \in \left\{ {0,1} \right\}} \\1 & {{{if}\mspace{14mu} p} \in \left\{ {2,3} \right\}}\end{matrix}m} = 0},1,\ldots \mspace{14mu},{{{2 \cdot N_{RB}^{DL}} - {1m^{\prime}}} = {{m + N_{RB}^{\max,{DL}} - {N_{RB}^{DL}v}} = \left\{ {{\begin{matrix}0 & {{{if}\mspace{14mu} p} = {{0\mspace{14mu} {and}\mspace{14mu} l} = 0}} \\3 & {{{if}\mspace{14mu} p} = {{0\mspace{14mu} {and}\mspace{14mu} l} \neq 0}} \\3 & {{{if}\mspace{14mu} p} = {{1\mspace{14mu} {and}\mspace{14mu} l} = 0}} \\0 & {{{if}\mspace{14mu} p} = {{1\mspace{14mu} {and}\mspace{14mu} l} \neq 0}} \\{3\left( {n_{s}\mspace{11mu} {mod}\; 2} \right)} & {{{if}\mspace{14mu} p} = 2} \\{3 + {3\left( {n_{s}\mspace{11mu} {mod}\; 2} \right)}} & {{{if}\mspace{14mu} p} = 3}\end{matrix}v_{shift}} = {N_{ID}^{cell}\; {mod}\; 6}} \right.}}} \right.}} & \left\lbrack {{Equation}\mspace{14mu} 12} \right\rbrack\end{matrix}$

In Equation 12, k and 1 denote a subcarrier index and a symbol index,respectively, and p denotes an antenna port. N_(symb) ^(DL) denotes thenumber of OFDM symbols in one downlink slot, and N_(RB) ^(DL) denotesthe number of radio resources allocated to downlink. n_(s) denotes aslot index, and N_(ID) ^(cell) denotes a cell ID. mod denotes modulooperation. The position of a reference signal is different depending ona value v_(shift) in a frequency domain. Since the value v_(shift)depends on a cell ID, the position of a reference signal has variousfrequency shift values depending on a cell.

More specifically, in order to improve channel estimation performancethrough a CRS, the position of a CRS may be shifted in a frequencydomain. For example, if reference signals are placed at an interval of 3subcarriers, reference signals in one cell are allocated to a 3k-thsubcarrier, and reference signals in the other cell are allocated to a(3k+1)-th subcarrier. From the point of view of a single antenna port,reference signals are arrayed at an interval of 6 resource elements in afrequency domain. Reference signals are spaced apart from referencesignals allocated in other antenna ports at an interval of 3 resourceelements.

In a time domain, reference signals are started from the symbol index 0of each slot and are arrayed at a constant interval. A time interval isdifferent defined depending on the length of a cyclic prefix. In thecase of a normal cyclic prefix, reference signals are placed in thesymbol indices 0 and 4 of a slot. In the case of an extended cyclicprefix, reference signals are placed in the symbol indices 0 and 3 of aslot. A reference signal for an antenna port that belongs to 2 antennaports and that has a maximum value is defined within one OFDM symbol.Accordingly, in the case of 4 transmission antenna transmission,reference signals for RS antenna ports 0 and 1 are placed in the symbolindices 0 and 4 of a slot (i.e., symbol indices 0 and 3 in the case ofan extended cyclic prefix), and reference signals for antenna ports 2and 3 are placed in the symbol index 1 of the slot. The positions ofreference signals for antenna ports 2 and 3 in a frequency domain arechanged in a second slot.

A DRS is described in more detail below. The DRS is used to demodulatedata. In multi-input/output antenna transmission, precoding weight usedfor specific UE is combined with a transport channel transmitted by eachtransmission antenna when the UE receives a reference signal and is usedto estimate a corresponding channel without any change.

A 3GPP LTE system (e.g., release-8) supports a maximum of 4 transmissionantennas and uses a DRS for rank 1 beamforming. The DRS for rank 1beamforming also indicates a reference signal for an antenna port index5.

A rule on which a DRS is mapped to a resource block is defined asfollows. Equation 13 illustrates a normal cyclic prefix, and Equation 14illustrates an extended cyclic prefix.

$\begin{matrix}{k = {{\left( k^{\prime} \right)\; {mod}\; N_{sc}^{RB}} + {N_{sc}^{RB} \cdot n_{PRB}}}} & \left\lbrack {{Equation}\mspace{14mu} 13} \right\rbrack \\{k^{\prime} = \left\{ \begin{matrix}{{4m^{\prime}} + v_{shift}} & {{{if}\mspace{14mu} l} \in \left\{ {2,3} \right\}} \\{{4m^{\prime}} + {\left( {2 + v_{shift}} \right){mod}\; 4}} & {{{if}\mspace{14mu} l} \in \left\{ {5,6} \right\}}\end{matrix} \right.} & \; \\{l = \left\{ \begin{matrix}3 & {l^{\prime} = 0} \\6 & {l^{\prime} = 1} \\2 & {l^{\prime} = 2} \\5 & {l^{\prime} = 3}\end{matrix} \right.} & \; \\{l^{\prime} = \left\{ \begin{matrix}{0,1} & {{{if}\mspace{14mu} n_{s}\; {mod}\; 2} = 0} \\{2,3} & {{{if}\mspace{14mu} n_{s}\; {mod}\; 2} = 1}\end{matrix} \right.} & \; \\{{m^{\prime} = 0},1,\ldots \mspace{14mu},{{3N_{RB}^{PDSCH}} - 1}} & \; \\{v_{shift} = {N_{ID}^{cell}\; {mod}\; 3}} & \; \\{k = {{\left( k^{\prime} \right){mod}\; N_{sc}^{RB}} + {N_{sc}^{RB} \cdot n_{PRB}}}} & \left\lbrack {{Equation}\mspace{14mu} 14} \right\rbrack \\{k^{\prime} = \left\{ \begin{matrix}{{3m^{\prime}} + v_{shift}} & {{{if}\mspace{14mu} l} = 4} \\{{3m^{\prime}} + {\left( {2 + v_{shift}} \right){mod}\; 3}} & {{{if}\mspace{14mu} l} = 1}\end{matrix} \right.} & \; \\{l = \left\{ \begin{matrix}4 & {l^{\prime} \in \left\{ {0,2} \right\}} \\1 & {l^{\prime} = 1}\end{matrix} \right.} & \; \\{l^{\prime} = \left\{ \begin{matrix}0 & {{{if}\mspace{14mu} n_{s}\; {mod}\; 2} = 0} \\{1,2} & {{{if}\mspace{14mu} n_{s}\; {mod}\; 2} = 1}\end{matrix} \right.} & \; \\{{m^{\prime} = 0},1,\ldots \mspace{14mu},{{4N_{RB}^{PDSCH}} - 1}} & \; \\{v_{shift} = {N_{ID}^{cell}\; {mod}\; 3}} & \;\end{matrix}$

In Equations 12 to 14, k and p denote a subcarrier index and an antennaport, respectively. denote the number of RBs allocated to downlink, thenumber of slot indices, and the number of cell IDs. The position of anRS is different depending on the value v_(shift) from the point of viewof a frequency domain.

In Equations 13 and 14, k and l denote a subcarrier index and a symbolindex, respectively, and p denotes an antenna port. N_(sc) ^(RB) denotesthe size of an RB in a frequency domain and is represented as the numberof subcarriers. n_(PRB) denotes the number of physical RBs. N_(RB)^(PDSCH) denotes the frequency bandwidth of an RB for PDSCHtransmission. n_(s) denotes the index of a slot, and N_(ID) ^(PDSCH)denotes the ID of a cell. mod denotes modulo operation. The position ofa reference signal is different depending on the value v_(shift) in afrequency domain. Since the value v_(shift) depends on the ID of a cell,the position of a reference signal has various frequency shift valuesdepending on a cell.

Sounding Reference Signal (SRS)

An SRS is mostly used in the measurement of channel quality in order toperform uplink frequency-selective scheduling and is not related to thetransmission of uplink data and/or control information, but the presentinvention is not limited thereto. The SRS may be used for various otherpurposes for improving power control or various startup functions of UEswhich have not been recently scheduled. The startup functions mayinclude an initial Modulation and Coding Scheme (MCS), initial powercontrol for data transmission, a timing advance, and frequencysemi-selective scheduling, for example. In this case, the frequencysemi-selective scheduling means selectively allocating a frequencyresource to the first slot of a subframe and pseudo-randomly hopping toanother frequency in the second slot of the subframe and allocatingfrequency resources.

Furthermore, the SRS may be used to measure downlink channel quality,assuming that a radio channel is reciprocal between uplink and downlink.Such an assumption is particularly valid when the same frequencyspectrum is shared between uplink and downlink and in Time DivisionDuplex (TDD) systems separated in a time domain.

The subframes of an SRS transmitted by UE within a cell may berepresented by a cell-specific broadcasting signal. A 4-bitcell-specific parameter “srsSubframeConfiguration” indicates 15available subframe arrays in which an SRS may be transmitted thoughrespective radio frames. In accordance with such arrays, the flexibilityof control of SRS overhead can be provided according to a deploymentscenario.

A sixteenth array completely turns off the switch of an SRS within acell, which is mostly suitable for a serving cell which provides serviceto high-speed UEs.

FIG. 16 illustrates an uplink subframe including the symbols of aSounding Reference Signal (SRS) in a wireless communication system towhich an embodiment of the present invention may be applied.

Referring to FIG. 16, an SRS is always transmitted through the lastSC-FDMA symbol in an arrayed subframe. Accordingly, an SRS and DMRS areplaced in different SC-FDMA symbols. The transmission of PUSCH data isnot permitted in a specific SC-FDMA symbol for SRS transmission. As aresult, if sounding overhead is the highest, that is, although an SRSsymbol is included in all subframes, sounding overhead does not exceedabout 7%.

Each SRS symbol is generated based on a base sequence (i.e., a randomsequence or a sequence set based on Zadoff-Ch (ZC)) regarding a giventime unit and frequency bandwidth. All UEs within the same cell use thesame base sequence. In this case, the transmissions of SRSs from aplurality of UEs within the same cell in the same frequency bandwidthand the same time are orthogonal to each other by different cyclicshifts of a base sequence and are distinguished from each other.

SRS sequences from different cells may be distinguished from each otherbecause different base sequences are allocated to respective cells, butorthogonality between the different base sequences is not guaranteed.

Coordinated Multi-Point (CoMP) Transmission and Reception

In line with the demand of LTE-advanced, there has been proposed CoMPtransmission in order to improve system performance. CoMP is also calledco-MIMO, collaborative MIMO, or network MIMO. CoMP is expected toimprove performance of UE located in a cell edge and to improve theaverage throughput of a cell (or sector).

In general, inter-cell interference deteriorates performance of UElocated in a cell edge and the average cell (or sector) efficiency in amulti-cell environment in which a frequency reuse factor is 1. In orderto reduce inter-cell interference, a simple passive method, such asFractional Frequency Reuse (FFR), has been applied to an LTE system sothat UE placed in a cell edge in an interference-limited environment hasproper performance efficiency. However, instead of reducing the use offrequency resources per cell, a method of reusing inter-cellinterference as a signal required to be received by UE or reducinginter-cell interference is more advantageous. In order to achieve theabove object, a CoMP transmission method may be used.

A CoMP method applicable to downlink may be divided into a JointProcessing (JP) method and a Coordinated Scheduling/Beamforming (CS/CB)method.

In the JP method, data may be used in each point (ie, eNB) of a CoMPunit. The CoMP unit means a set of eNBs used in the CoMP method. The JPmethod may be subdivided into a joint transmission method and a dynamiccell selection method.

The joint transmission method is a method of transmitting, by aplurality of points, that is, some or all of the points of a CoMP unit,signals through a PDSCH at the same time. That is, data transmitted toone UE is transmitted from a plurality of transmission points at thesame time. The quality of a signal transmitted to UE can be improvedcoherently or non-coherently and interference between the UE and anotherUE can be actively removed through such a joint transmission method.

The dynamic cell selection method is a method of sending a signal by onepoint of a CoMP unit through a PDSCH. That is, data transmitted to oneUE on a specific time is transmitted from one point, but is nottransmitted from another point within the CoMP unit to the UE. A pointat which data is transmitted to UE may be dynamically selected.

In accordance with the CS/CB method, a CoMP unit performs beamforming incooperation in order to send data to one UE. That is, data istransmitted to UE in a serving cell only, but userscheduling/beamforming may be determined through cooperation between aplurality of cells within a CoMP unit.

In some embodiments, CoMP reception means the reception of a signaltransmitted by cooperation between a plurality of points that aregeographically separated. A CoMP method which may be applied to uplinkmay be divided into a Joint Reception (JR) method and a CoordinatedScheduling/Beamforming (CS/CB) method.

The JR method is a method of receiving, by a plurality of points, thatis, some or all of the points of a CoMP unit, a signal transmittedthrough a PDSCH. In the CS/CB method, a signal transmitted through aPDSCH is received only at one point, but user scheduling/beamforming maybe determined through cooperation between a plurality of cells within aCoMP unit.

Relay Node (RN)

In a relay node, data transmitted/received between an eNB and UE istransferred through two different links (i.e., a backhaul link and anaccess link). An eNB may include a donor cell. A relay node iswirelessly connected to a radio access network through a donor cell.

In relation to the use of the bandwidth (or spectrum) of a relay node, acase where a backhaul link operates in the same frequency bandwidth asthat of an access link is called an “in-band”, and a case where abackhaul link and an access link operate in different frequencybandwidths is called an “out-band.” In both the in-band and theout-band, UE (hereinafter called “legacy UE”) operating in accordancewith an existing LTE system (e.g., release-8) needs to be able to accessa donor cell.

A relay node may be divided into a transparent relay node and anon-transparent relay node depending on whether UE recognizes a relaynode. The term “transparent” means whether UE communicates with anetwork through a relay node is not recognized. The term“non-transparent” means whether UE communicates with a network through arelay node is recognized.

In relation to control of a relay node, a relay node may be divided intoa relay node formed as part of a donor cell and a relay nodeautonomously controlling a cell.

A relay node formed as part of a donor cell may have a relay nodeidentity (relay ID), but does not have its own cell identity.

If at least part of Radio Resource Management (RRM) is controlled by aneNB belonging to a donor cell, it is called a relay node formed as partof a donor cell although the remaining parts of the RRM are placed inthe relay node. Such a relay node may support legacy UE. For example,various types of smart repeaters, decode-and-forward relays, and secondlayer (L2) relay nodes and a Type-2 relay node correspond to such arelay node.

In the case of a relay node autonomously controlling a cell, the relaynode controls one or a plurality of cells, and a unique physical layercell identity is provided to each of the cells controlled by the relaynode. Furthermore, the cells controlled by the relay node may use thesame RRM mechanism. From a viewpoint of UE, there is no differencebetween access to a cell controlled by a relay node and access to a cellcontrolled by a common eNB. A cell controlled by such a relay node cansupport legacy UE. For example, a self-backhauling relay node, a thirdlayer (L3) relay node, a Type-1 relay node, and a Type-1a relay nodecorrespond to such a relay node.

The Type-1 relay node is an in-band relay node and controls a pluralityof cells, and each of the plurality of cells is seen by UE as a separatecell different from a donor cell. Furthermore, the plurality of cellshas different physical cell IDs (this is defined in LTE release-8), andthe relay node may send its own synchronization channel and referencesignal. In the case of one cell operation, UE directly may receivescheduling information and HARQ feedback from a relay node and send itsown control channels (e.g., a Scheduling Request (SR), a CQI, andACK/NACK) to the relay node. Furthermore, the Type-1 relay node is seenby legacy UE (i.e., UE operating in accordance with an LTE release-8system) as a legacy eNB (i.e., an eNB operating in accordance with anLTE release-8 system). That is, the Type-1 relay node has backwardcompatibility. Meanwhile, the Type-1 relay node is seen by UEs operatingin accordance with an LTE-A system as an eNB different from a legacyeNB, thereby being capable of providing improved performance.

The Type-1a relay node has the same characteristics as the Type-1 relaynode except that it operates in an out-band. The operation of theType-1a relay node may be configured so that an influence on a firstlayer (L1) operation is minimized.

The Type-2 relay node is an in-band relay node, and it does not have aseparate physical cell ID and thus does not form a new cell. The Type-2relay node is transparent to legacy UE, and the legacy UE does notrecognize the presence of the Type-2 relay node. The Type-2 relay nodemay send a PDSCH, but does not send at least CRS and PDCCH.

In order to prevent a relay node from operating in in-band, someresources in a time-frequency domain may need to be reserved for abackhaul link and may be configured so that they are not used for anaccess link. This is called resource partitioning.

A known principle in resource partitioning in a relay node may bedescribed as follows. Backhaul downlink and access downlink may bemultiplexed according to a Time Division Multiplexing (TDM) method onone carrier frequency (i.e., only one of a backhaul downlink and anaccess downlink in a specific time is activated). Likewise, backhauluplink and access uplink may be multiplexed according to a TDM method onone carrier frequency (i.e., only one of a backhaul uplink and an accessuplink in a specific time is activated).

In backhaul link multiplexing in FDD, backhaul downlink transmission maybe performed in a downlink frequency bandwidth, and the transmission ofa backhaul uplink may be performed in an uplink frequency bandwidth. Inbackhaul link multiplexing in TDD, backhaul downlink transmission may beperformed in a downlink subframe of an eNB and a relay node, and thetransmission of a backhaul uplink may be performed in an uplink subframeof an eNB and a relay node.

In the case of an in-band relay node, for example, when the reception ofa backhaul downlink from an eNB and the transmission of an accessdownlink to UE are performed in the same frequency bandwidth at the sametime, signal interference may be generated in the reception end of arelay node due to a signal transmitted by the transmission end of therelay node. That is, signal interference or RF jamming may be generatedin the RF front end of the relay node. Likewise, when the transmissionof a backhaul uplink to an eNB and the reception of an access uplinkfrom UE are performed in the same frequency bandwidth at the same time,signal interference may be generated.

Accordingly, in order for a relay node to send/receive signals in thesame frequency bandwidth at the same time, a sufficient separation needsto be provided between a reception signal and a transmission signal(e.g., that the reception signal and the transmission signal need to besufficiently separated geographically, such as that a transmissionantenna and a reception antenna are installed on the ground and in thegrave, respectively).

One method for solving such signal interference is to allow a relay nodeto operate in such a way as not to send a signal to UE while receiving asignal from a donor cell. That is, a gap is generated in transmissionfrom the relay node to the UE, and the UE (including legacy UE) isconfigured to not expect any transmission from the relay node during thegap. Such a gap may be configured by configuring a Multicast BroadcastSingle Frequency Network (MBSFN) subframe.

FIG. 17 illustrates the segmentation of a relay node resource in awireless communication system to which an embodiment of the presentinvention may be applied.

In FIG. 17, a first subframe is a common subframe, and a downlink (i.e.,access downlink) control signal and data are transmitted from a relaynode to UE in the first subframe. In contrast, a second subframe is anMBSFN subframe, and a control signal is transmitted from the relay nodeto the UE in the control region of the downlink subframe, but notransmission is performed from the relay node to the UE in the remainingregion of the downlink subframe. In this case, since legacy UE expectsthe transmission of a PDCCH in all downlink subframes (i.e., a relaynode needs to provide support so that legacy UEs within the region ofthe relay node perform measurement functions by receiving a PDCCH everysubframe), the PDCCH needs to be transmitted in all downlink subframesfor the correct operation of the legacy UE. Accordingly, the relay nodedoes not perform backhaul downlink reception, but needs to performaccess downlink transmission in the first N (N=1, 2 or 3) OFDM symbolperiod of a subframe (i.e., the second subframe) on the subframeconfigured for downlink (i.e., backhaul downlink) transmission from aneNB to the relay node. For this, the relay node may provide backwardcompatibility to serving legacy UE because a PDCCH is transmitted fromthe relay node to the UE in the control region of the second subframe.The relay node may receive transmission from the eNB while notransmission is performed from the relay node to the UE in the remainingregion of the second subframe. Accordingly, access downlink transmissionand backhaul downlink reception may not be performed at the same time inan in-band relay node through such a resource partitioning method.

The second subframe using an MBSFN subframe is described in detail. Thecontrol region of the second subframe may be said to be a relay nodenon-hearing period. The relay node non-hearing interval means aninterval in which a relay node does not receive a backhaul downlinksignal, but sends an access downlink signal. The interval may beconfigured to have a 1, 2 or 3 OFDM length, such as that describedabove. A relay node performs access downlink transmission to UE in arelay node non-hearing interval, but may perform backhaul downlinkreception from an eNB in the remaining region. In this case, time istaken for the relay node to switch from transmission mode to receptionmode because the relay node is unable to perform transmission/receptionin the same frequency bandwidth at the same time. Accordingly, a GuardTime (GP) needs to be configured so that the relay node switches totransmission/reception mode in the first some interval of a backhauldownlink reception region. Likewise, a guard time for enabling the relaynode to switch to reception/transmission mode may be configured althoughthe relay node operates in such a way as to receive a backhaul downlinkfrom the eNB and to send an access downlink to the UE. The length ofsuch a guard time may be set as a value in a time domain. For example,the length of the guard time may be set as a k (k≧1) time sample (Ts)value or may be set as one or more OFDM symbol length. Alternatively,relay node backhaul downlink subframes may be contiguously configured,or the guard time of the last part of a subframe may not be defined orconfigured according to a specific subframe timing alignmentrelationship. Such a guard time may be defined only in a frequencydomain configured for backhaul downlink subframe transmission in orderto maintain backward compatibility (if a guard time is configured in anaccess downlink interval, legacy UE cannot be supported). In a backhauldownlink reception interval other than the guard time, the relay nodecan receive a PDCCH and a PDSCH from the eNB. This may be represented bya relay-PDCCH (R-PDCCH) and a relay-PDSCH (R-PDSCH) in the meaning of arelay node-dedicated physical channel.

Channel State Information (CSI) Feedback

An MIMO method may be divided into an open-loop method and a closed-loopmethod. In the open-loop method, a transmission end performs MIMOtransmission without the feedback of CSI from an MIMO reception end. Inthe closed-loop MIMO method, a transmission end receives CSI fed back byan MIMO reception end and performs MIMO transmission. In the closed-loopMIMO method, in order to obtain the multiplexing gain of an MIMOtransmission antenna, each of a transmission end and a reception end mayperform beamforming based on CSI. A transmission end (e.g., an eNB) mayallocate an uplink control channel or an uplink shared channel to areception end (e.g., UE) so that a reception end (e.g., UE) is able tofeed CSI back.

The feedback CSI may include a Rank Indicator (RI), a Precoding MatrixIndex (PMI), and a Channel Quality Indicator (CQI).

The RI is information about a channel rank. The channel of a rank meansa maximum number of layers (or streams) in which different informationmay be transmitted through the same time-frequency resource. A rankvalue may be fed back in a longer cycle (i.e., less frequently) than aPMI and CQI because it is mostly determined by long term fading of achannel.

The PMI is information about a precoding matrix which is used intransmission from a transmission end and is a value into which thespatial characteristic of a channel is reflected. The term “precoding”means that a transmission layer is mapped to a transmission antenna, anda layer-antenna mapping relationship may be determined based on aprecoding matrix. The PMI corresponds to the PMI of an eNB, which ispreferred by UE based on a metric, such as a Signal-to-Interference plusNoise Ratio (SINR). In order to reduce feedback overhead of precodinginformation, a method of previously sharing, by a transmission end and areception end, a codebook including several precoding matrices andfeeding only an index indicative of a specific precoding matrix in thecorresponding codebook back may be used.

The CQI is information indicative of the intensity of channel or qualityof channel. The CQI may be represented as a predetermined MCScombination. That is, a CQI index that is fed back is indicative of acorresponding modulation scheme and coding rate. In general, the CQI isa value into which a reception SINR which may be obtained when an eNBconfigures a space channel using a PMI is reflected.

In a system (e.g., LTE-A system) supporting an extended antennaconfiguration, to obtain additional multi-user diversity using amulti-user-MIMO (MU-MIMO) method is taken into consideration. In theMU-MIMO method, an interference channel is present between UEsmultiplexed in an antenna region. Accordingly, it is necessary toprevent interference from occurring in another UE if an eNB performsdownlink transmission using CSI fed back by one UE of multiple users.Accordingly, in order for an MU-MIMO operation to be correctlyperformed, CSI having higher accuracy compared to a single user-MIMO(SU-MIMO) method needs to be fed back.

A new CSI feedback method using improved CSI including an existing RI,PMI, and CQI may be used so that more accurate CSI can be measured andreported as described above. For example, precoding information fed backby a reception end may be indicated by a combination of two PMIs. One(the first PMI) of the two PMIs has the attributes of a long term and/ora wideband and may be called W1. The other (the second PMI) of the twoPMIs has the attributes of a short term and/or a sub-band and may becalled W2. The final PMI may be determined by a combination (orfunction) of W1 and W2. For example, assuming that the final PMI is W,W=W1*W2 or W=W2*W1 may be defined.

In this case, the average characteristics of a channel in terms of thefrequency and/or time are reflected in W1. In other words, W1 may bedefined as CSI in which the characteristics of a long term channel interms of time are reflected, the characteristics of a wideband channelin terms of frequency are reflected, or the characteristics of a longterm channel in terms of time and a wideband channel in terms offrequency are incorporated. In order to simply represent suchcharacteristics of W1, W1 is called CSI of long term-wideband attributes(or a long term wideband PMI).

A channel characteristic that is instantaneous compared to W1 isreflected in W2. In other words, W2 may be defined as CSI in which thecharacteristics of a short term channel in terms of time are reflected,the characteristics of a sub-band channel in terms of frequency arereflected, or the characteristics of a short term channel in terms oftime and a sub-band channel in terms of frequency are reflected. Inorder to simply represent such characteristics of W2, W2 is called CSIof a short term-sub-band attributes (or a short term sub-band PMI).

In order for one final precoding matrix W to be determined based oninformation about 2 different attributes (e.g., W1 and W2) indicative ofa channel state, it is necessary to configure a separate codebookincluding precoding matrices indicative of channel information aboutattributes (i.e., a first codebook for W1 and a second codebook for W2).The form of a codebook configured as described above may be called ahierarchical codebook. Furthermore, to determine a codebook to befinally used using the hierarchical codebook may be called hierarchicalcodebook transformation.

If such a codebook is used, channel feedback of higher accuracy comparedto a case where a single codebook is used is made possible. Single cellMU-MIMO and/or multi-cell cooperation communication may be supportedusing channel feedback of higher accuracy as described above.

Enhanced PMI for MU-MIMO or CoMP

In a next-generation communication standard, such as LTE-A, there hasbeen proposed transmission schemes, such as MU-MIMO and CoMP, in orderto achieve a high transfer rate. In order to implement such improvedtransmission schemes, UE needs to feed more complicated and various CSIback to an eNB.

For example, in MU-MIMO, a CSI feedback method of uploading, by UE-A,the PMI (hereinafter called a “best companion PMI (BCPMI)”) of UE to bescheduled along with the UE-A, together with the desired PMI of theUE-A, when the UE-A selects a PMI is taken into consideration.

That is, when co-scheduled UE is used as a precoder in a precodingmatrix codebook, it calculates a BCPMI that provides less interferenceto UE-A and additionally feeds the calculated BCPMI back to an eNB.

The eNB schedules the UE-A and another UE which prefers BCPM (BestCompanion Precoding Matrix (BCPM) corresponding to a BCPMI) precodingusing the information.

A BCPMI feedback method is divided into explicit feedback and implicitfeedback depending on whether feedback payload is present or not.

First, there is an explicit feedback method having feedback payload.

In the explicit feedback method, UE-A determines a BCPMI within aprecoding matrix codebook and feeds the BCPMI back to an eNB through acontrol channel. In one method, UE-A may select an interference signalprecoding matrix that maximizes an estimated SINR within a codebook andfeed the interference signal precoding matrix back as a BCPMI value.

An advantage of the explicit feedback method is to select a BCPMI moreeffective in removing interference and to send the selected BCPMI. Thereason for this is that, assuming that each of all codewords within acodebook is one interference beam, UE determines a value most effectivein removing interference to be a BCPMI by performing comparison onmetrics, such as SINRs. A greater feedback payload size is requiredbecause candidate BCPMIs are increased as a codebook size is increased.

Second, there is an implicit feedback method not having feedbackpayload.

In the implicit feedback method, UE-A does not search a codebook for acodeword having the least interference and select the retrieved codebookas a BCPMI, but a corresponding BCPMI is statically determined once adesired PMI is determined. In this case, a BCPMI may include vectorsorthogonal to the determined desired PMI.

The reason for this is that it is effective to reduce interference froman interference signal when desired PM is selected in directions otherthan the direction of a PM because the desired PM has been configured inthe direction in which the channel gain of a channel H can be maximizedin order to maximize a reception SINR. If the channel H is analyzed as aplurality of independent channels through Singular Value Decomposition(SVD), such a BCPMI decision method is further justified. A 4×4 channelH may be decomposed through SVD as in Equation 15 below.

$\begin{matrix}{H = {{ULV}^{H} = {{\begin{bmatrix}u_{1} & u_{2} & u_{3} & u_{4}\end{bmatrix}\begin{bmatrix}\lambda_{1} & 0 & 0 & 0 \\0 & \lambda_{2} & 0 & 0 \\0 & 0 & \lambda_{3} & 0 \\0 & 0 & 0 & \lambda_{4}\end{bmatrix}}\begin{bmatrix}v_{1}^{H} \\v_{2}^{H} \\v_{3}^{H} \\v_{4}^{H}\end{bmatrix}}}} & \left\lbrack {{Equation}\mspace{14mu} 15} \right\rbrack\end{matrix}$

In Equation 15, U, V is a unitary matrix. u_(i), v_(i), and λ_(i) arethe 4×1 left singular vector, 4×1 right singular vector, and singularvalue of a channel H and are arranged in λ_(i)>λ_(i+1) in descendingorder. All channel gains which may be theoretically obtained if abeamforming matrix V is used in a transmission end and a beamformingmatrix U^(H) is used in a reception end can be obtained without a loss.

In the case of a rank 1, optimal performance may be obtained from thepoint of view of an SNR because a channel gain |λ_(i)|² is obtained whena transmission beamforming vector v₁ and a reception beamforming vectoru1 are used. For example, it is advantage for UE-A to select a PM mostsimilar to v₁ in the case of a rank 1. If a desired PM is ideallymatched up with v₁, an interference signal can be perfectly removedwithout a loss of a desired signal by setting a reception beam as u₁ andsetting the transmission beam of the interference signal in a directionorthogonal to the PM. If there is some difference between a desired PMand v₁ due to a quantization error, however, an interference signal maynot be perfectly removed without a loss of a desired signal because thetransmission beam of the interference signal set in the directionorthogonal to the PM is no longer the same as a beam orthogonal to v₁,but it may help control the interference signal if the quantizationerror is small.

As an example of implicit feedback, if an LTE codebook is used, a BCPMImay be statically determined to be a vector index orthogonal to a PMI.

In this case, it has been assumed that the number of transmissionantennas is 4 and UE which has fed the PMI back has a reception rank of1, and 3 vectors orthogonal to a desired PMI are represented as 3BCPMIs.

For example if a PMI is 3, a BCPMI is determined to be 0, 1, or 2. ThePMI and the BCPMI are indicative of the indices of a 4×1 vector codewordwithin a codebook. An eNB considers the BCPMI set (BCPMI=0, 1, 2) to bea valid precoding index for removing interference and uses some of orthe entire BCPMI set as the precoder of co-schedule UE.

An advantage of an implicit PMI is that there is no additional feedbackoverhead because a desired PMI and a BCPMI set are mapped in a 1:1 way.However, a BCPM dependent on desired PM may have an error in thedirection of an optimal interference removal beam due to thequantization error of the desired PM (i.e., a precoding matrixcorresponding to a PMI). If a quantization error is not present, all 3BCPMs represent interference beams (ideal interference beams) forperfectly removing interference. If a quantization error is present,however, there is a difference between the beam of each of the 3 BCPMsand an ideal interference beam.

Furthermore, a difference between the ideal interference beams of theBCPMs is the same in average, but may be different on a specific moment.For example, if a desired PMI=3, it may be effective to remove aninterference signal in order of BCPMIs 0, 1, and 2. In this case, thereis a possibility that an eNB unaware of a relative error between theBCPMIs 0, 1, and 2 may determine the BCPMI 2 having the greatest errorwith an ideal interference beam to be the beam of an interference signaland may perform communication in the state in which strong interferenceis present between co-scheduled UEs.

General D2D communication

In general, D2D communication is limitedly used as a term indicative ofcommunication between things or thing intelligence communication. In anembodiment of the present invention, however, D2D communication mayinclude all types of communication between a variety of types of deviceshaving a communication function, such as smart phones and personalcomputers, in addition to simple devices having a communicationfunction.

FIG. 18 is a diagram conceptually illustrating D2D communication in awireless communication system to which an embodiment of the presentinvention may be applied.

FIG. 18a shows an existing communication method based on an eNB. UE1 maysend data to an eNB in uplink, and the eNB may send data to UE2 indownlink. Such a communication method may be called an indirectcommunication method through an eNB. An Un link (i.e., a link betweeneNBs or a link between an eNB and a relay node, which may be called abackhaul link), that is, a link defined in an existing wirelesscommunication system, and/or an Uu link (i.e., a link between an eNB andUE or a link between a relay node and UE, which may be called an accesslink) may be related to the indirect communication method.

FIG. 18b shows a UE-to-UE communication method, that is, an example ofD2D communication. The exchange of data between UEs may be performedwithout the intervention of an eNB. Such a communication method may becalled a direct communication method between devices. The D2D directcommunication method has advantages of reduced latency and the use oflesser radio resources compared to the existing indirect communicationmethod through an eNB.

FIG. 19 shows an example of various scenarios of D2D communication towhich a method proposed in this specification may be applied.

A scenario for D2D communication may be basically divided into (1) anout-of-coverage network, (2) a partial-coverage network, and (3) anin-coverage network depending on where UE1 and UE2 are placed withincell coverage (i.e., in-coverage) and out of cell coverage (i.e.out-of-coverage).

The in-coverage network may be divided into an in-coverage-single-celland an in-coverage-multi-cell depending on the number of cellscorresponding to coverage of an eNB.

FIG. 19(a) shows an example of an out-of-coverage network scenario forD2D communication.

The out-of-coverage network scenario means that D2D communication isperformed between D2D UEs without control of an eNB.

From FIG. 19(a), it may be seen that only UE1 and UE2 are present andthe UE1 and the UE2 perform direct communication.

FIG. 19(b) shows an example of a partial-coverage network scenario forD2D communication.

The partial-coverage network scenario means that D2D communication isperformed between D2D UE placed within network coverage and D2D UEplaced out of the network coverage.

From FIG. 19(b), it may be seen that UE1 placed within network coverageand UE2 placed out of the network coverage perform communication.

FIG. 19(c) shows an example of an in-coverage-single-cell scenario, andFIG. 19(d) shows an example of an in-coverage-multi-cell scenario.

The in-coverage network scenario means that D2D UEs perform D2Dcommunication through control of an eNB within network coverage.

In FIG. 19(c), UE1 and UE2 are placed within the same network coverage(or cell) and perform D2D communication under the control of an eNB.

In FIG. 19(d), UE1 and UE2 are placed within network coverage, but areplaced within different network coverage. Furthermore, the UE1 and theUE2 perform D2D communication under the control of eNBs managing each ofnetwork coverage.

D2D communication is described in more detail below.

D2D communication may be performed in the scenarios of FIG. 19, but maybe commonly performed within network coverage (in-coverage) and out ofnetwork coverage (out-of-coverage). A link used for D2D communication(i.e., direct communication between UEs) may be called a D2D link, adirectlink, or a sidelink, but is hereinafter generally called asidelink, for convenience of description.

Sidelink transmission may be performed in an uplink spectrum in the caseof FDD and may be performed in an uplink (or downlink) subframe in thecase of TDD. Time Division Multiplexing (TDM) may be used for themultiplexing of sidelink transmission and uplink transmission.

Sidelink transmission and uplink transmission are not occured at thesame time. Sidelink transmission is not occured in a sidelink subframewhich partially or generally overlaps an uplink subframe or UpPTS usedfor uplink transmission. Furthermore, the transmission and reception ofa sidelink are also not occured at the same time.

The structure of an uplink physical resource may be identically used asthe structure of a physical resource used for sidelink transmission.However, the last symbol of a sidelink subframe includes a guard periodand is not used for sidelink transmission.

A sidelink subframe may include an extended Cyclic Prefix (CP) or anormal CP.

D2D communication may be basically divided into discovery, directcommunication, and synchronization.

1) Discovery

D2D discovery may be applied within network coverage (including aninter-cell and an intra-cell). In inter-cell discovery, both synchronousand asynchronous cell deployments may be taken into consideration. D2Ddiscovery may be used for various commercial purposes, such asadvertising, issuing coupons, and finding friends, to UE within aproximity region.

If UE 1 has a role of sending a discovery message, the UE 1 sends adiscovery message, and UE 2 receives the discovery message. Thetransmission and reception roles of the UE 1 and the UE 2 may bechanged. Transmission from the UE 1 may be received by one or moreUE(s), such as the UE 2.

The discovery message may include a single MAC PDU. In this case, thesingle MAC PDU may include a UE ID and an application ID.

A physical sidelink discovery channel (PSDCH) may be defined as achannel for sending the discovery message. The structure of a PUSCH maybe reused as the structure of the PSDCH.

Two types Type 1 and Type 2 may be used as a resource allocation methodfor D2D discovery.

In the case of Type 1, an eNB may allocate a resource for sending adiscovery message in a non-UE-specific way.

Specifically, a radio resource pool for discovery transmission andreception, including a plurality of subframes, is allocated in aspecific cycle. Discovery transmission UE randomly selects a specificresource from the radio resource pool and then sends a discoverymessage.

Such a periodic discovery resource pool may be allocated for discoverysignal transmission semi-statically. Information about the configurationof the discovery resource pool for discovery signal transmissionincludes a discovery cycle and the number of subframes (i.e., the numberof subframes forming the radio resource pool) which may be used to senda discovery signal within a discovery cycle.

In the case of in-coverage UE, a discovery resource pool for discoverytransmission may be configured by an eNB, and the in-coverage UE may benotified of the configured discovery resource pool through RRC signaling(e.g., a System Information Block (SIB)).

A discovery resource pool allocated for discovery within one discoverycycle may be TDM- and/or FDM-multiplexed as a time-frequency resourceblock having the same size. Such a time-frequency resource block havingthe same size may be called a “discovery resource.”

A discovery resource may be used for a single UE to send a discovery MACPDU. The transmission of an MAC PDU transmitted by a single UE may berepeated within a discovery cycle (i.e., a radio resource pool)continuously or discontinuously (e.g., four times). UE may randomlyselect a first discovery resource in a discovery resource set which maybe used for the repetitive transmission of an MAC PDU and may determinethe remaining discovery resources in relation to the first discoveryresource. For example, a specific pattern may be previously determined,and a next discovery resource may be determined according to thepredetermined specific pattern depending on the position of a discoveryresource first selected by UE. Alternatively, UE may randomly selecteach discovery resource within a discovery resource set which may beused for the repetitive transmission of an MAC PDU.

In the case of Type 2, a resource for discovery message transmission isallocated in a UE-specific way. Type 2 is subdivided into Type-2A andType-2B. Type-2A is a method of allocating, by an eNB, a resource at theinstance at which UE sends a discovery message within a discovery cycle,and Type-2B is a method of allocating resources semi-persistently.

In the case of Type-2B, RRC_CONNECTED UE requests an eNB to allocate aresource for the transmission of a D2D discovery message through RRCsignaling. Furthermore, the eNB may allocate the resource through RRCsignaling. When the UE transits to an RRC_IDLE state or when the eNBwithdraws resource allocation through RRC signaling, the UE releases themost recently allocated transmission resource. As described above, inthe case of Type-2B, a radio resource may be allocated through RRCsignaling, and the activation/deactivation of an allocated radioresource may be determined by a PDCCH.

A radio resource pool for receiving a discovery message may beconfigured by an eNB, and UE may be notified of the configured radioresource pool through RRC signaling (e.g., a System Information Block(SIB)).

Discovery message reception UE monitors both the aforementioneddiscovery resource pools of Type 1 and Type 2 in order to receive adiscovery message.

2) Direct Communication

The region to which D2D direct communication is applied includes anetwork coverage edge area (i.e., edge-of-coverage) in addition toinside and outside network coverage (i.e., in-coverage andout-of-coverage). D2D direct communication may be used for purposes,such as Public Safety (PS).

If UE 1 has a role of direct communication data transmission, the UE 1sends direct communication data, and UE 2 receives the directcommunication data. The transmission and reception roles of the UE 1 andthe UE 2 may be changed. The direct communication transmission from theUE 1 may be received by one or more UE(s), such as the UE 2.

D2D discovery and D2D communication may be independently defined withoutbeing associated with each other. That is, in groupcast and broadcastdirect communication, D2D discovery is not required. If D2D discoveryand D2D direct communication are independently defined as describedabove, UEs do not need to perceive adjacent UE. In other words, in thecase of groupcast and broadcast direct communication, all reception UEswithin a group are not required to be adjacent to each other.

A physical sidelink shared channel (PSSCH) may be defined as a channelfor sending D2D direct communication data. Furthermore, a physicalsidelink control channel (PSCCH) may be defined as a channel for sendingcontrol information (e.g., Scheduling Assignment (SA), a transmissionformat for direct communication data transmission, etc) for D2D directcommunication. The structure of a PUSCH may be reused as the structuresof the PSSCH and the PSCCH.

Two types of mode 1 and mode 2 may be used as a resource allocationmethod for D2D direct communication. Mode 1 refers to a method ofscheduling, by an eNB, data for D2D direct communication by UE or aresource used for UE to send control information. Mode 1 is applied toin-coverage.

An eNB configures a resource pool for D2D direct communication. In thiscase, the resource pool for D2D communication may be divided into acontrol information pool and a D2D data pool. When an eNB schedulescontrol information and a D2D data transmission resource within a poolconfigured for transmission D2D UE using a PDCCH or ePDCCH, thetransmission D2D UE sends control information and D2D data using theallocated resource.

Transmission UE requests a transmission resource from an eNB. The eNBschedules a resource for sending control information and D2D directcommunication data. That is, in the case of mode 1, the transmission UEneeds to be in the RRC_CONNECTED state in order to perform D2D directcommunication. The transmission UE sends a scheduling request to theeNB, and a Buffer Status Report (BSR) procedure is performed so that theeNB may determine the amount of resources requested by the transmissionUE.

Reception UEs monitors a control information pool. When decoding controlinformation related to reception UE, the reception UE may selectivelydecode D2D data transmission related to corresponding controlinformation. The reception UE may not decode a D2D data pool based on aresult of the decoding of the control information.

Mode 2 refers to a method of randomly selecting, by UE, a specificresource in a resource pool in order to send data or control informationfor D2D direct communication. Mode 2 is applied to out-of-coverageand/or edge-of-coverage.

In mode 2, a resource pool for sending control information and/or aresource pool for sending D2D direct communication data may bepre-configured or may be configured semi-statically. UE is supplied witha configured resource pool (time and frequency) and selects a resourcefor D2D communication transmission in the resource pool. That is, the UEmay select a resource for control information transmission in a controlinformation resource pool in order to send control information.Furthermore, the UE may select a resource in a data resource pool inorder to send D2D direct communication data.

In D2D broadcast communication, control information is transmitted bybroadcasting UE. Control information is explicitly and/or implicitlyindicative of the position of a resource for data reception in relationto a physical channel (i.e., a PSSCH) on which D2D direct communicationdata is carried.

3) Synchronization

A D2D synchronization signal (or a sidelink synchronization signal) maybe used for UE to obtain time-frequency synchronization. In particular,since control of an eNB is impossible in the case of out-of-networkcoverage, a new signal and procedure for establishing synchronizationbetween UEs may be defined.

UE which periodically sends a D2D synchronization signal may be called aD2D synchronization source. If a D2D synchronization source is an eNB, atransmitted D2D synchronization signal may have the same structure as aPSS/SSS. If a D2D synchronization source is not an eNB (e.g., UE or aGlobal Navigation Satellite System (GNSS)), the structure of atransmitted D2D synchronization signal may be newly defined.

A D2D synchronization signal is periodically transmitted in a cycle notless than 40 ms. UE may have multiple physical layer sidelinksynchronization identities. A D2D synchronization signal includes aprimary D2D synchronization signal (or a primary sidelinksynchronization signal) and a secondary D2D synchronization signal (or asecondary sidelink synchronization signal).

UE may search for a D2D synchronization source before it sends a D2Dsynchronization signal. Furthermore, when the D2D synchronization sourceis searched for, the UE may obtain time-frequency synchronizationthrough a D2D synchronization signal received from the retrieved D2Dsynchronization source. Furthermore, the UE may send a D2Dsynchronization signal.

In D2D communication, direct communication between two devices isdescribed below as an example, for clarity, but the scope of the presentinvention is not limited thereto. The same principle described in anembodiment of the present invention may be applied to D2D communicationbetween a plurality of two or more devices.

Determination of RS (UE Signal)-Aided Discovery Resource

A discovery resource decision method using an RS proposed in thisspecification is proposed.

As described above, one of D2D discovery methods includes a method(hereinafter called “distributed discovery”) of performing, by all UEs,discovery in a distributed way. The method of performing distributed D2Ddiscovery means a method of autonomously determining, by all UEs,discovery resources and sending and receiving discovery messages unlikea method of determining resource selection at one place (e.g., an eNB,UE, or a D2D scheduling device) as in a centralized method.

In this application, a signal (or message) periodically transmitted byUEs for D2D discovery may be hereinafter called a discovery message,discovery signal, or beacon. The signal is generally called a discoverymessage, for convenience of description.

In distributed discovery, a dedicated resource may be periodicallyallocated as a resource for allowing UE to send and receive a discoverymessage, separately from a cellular resource. This is described belowwith reference to FIG. 21.

FIG. 20 shows an example in which discovery resources have beenallocated according to an embodiment of the present invention.

Referring to FIG. 20, in the distributed discovery method, a discoverysubframe (i.e., a “discovery resource pool”) 2001 for discovery in allcellular uplink frequency-time resources is allocated fixedly (ordedicatedly), and the remaining region may consist of an existing LTEuplink Wide Area Network (WAN) subframe region 2003. The discoveryresource pool may include one or more subframes.

The discovery resource pool may be periodically allocated at a specifictime interval (i.e., “discovery cycle”). Furthermore, the discoveryresource pool may be repeatedly configured within one discovery cycle.

FIG. 20 shows an example in which a discovery resource pool is allocatedin a discovery cycle of 10 sec and 64 contiguous subframes are allocatedto each discovery resource pool, but a discovery cycle and the size oftime/frequency resources of a discovery resource pool are not limitedthereto.

UE autonomously selects a resource (i.e., “discovery resource”) forsending its discovery message in a dedicated allocated discovery pooland sends the discovery message through the selected resource. This isdescribed below with reference to FIG. 21.

FIG. 21 is a simplified diagram illustrating a discovery processaccording to an embodiment of the present invention.

Referring to FIGS. 20 and 21, a discovery method basically includes a3-step procedure, such as a resource sensing step S2101 for discoverymessage transmission, a resource selection step S2103 for discoverymessage transmission, and a discovery message transmission and receptionstep S2105.

First, in the resource sensing step S2101 for discovery messagetransmission, all UEs performing D2D discovery receive (i.e., sense) alldiscovery messages in a distributed way (i.e., autonomously) during 1cycle (period) of a D2D discovery resource (i.e., a discovery resourcepool). For example, assuming that an uplink bandwidth is MHz in FIG. 20,all UEs receive (i.e., sense) all discovery messages transmitted in N=44RBs (6 RBs of a total of 50 RBs are used for PUCCH transmission becausethe entire uplink bandwidth is 10 MHz) during K=64 msec (64 subframes).

Furthermore, in the resource selection step S2103 for discovery messagetransmission, UE selects resources that belong to the sensed resourcesand that have a low energy level and randomly selects a discoveryresource within a specific range (e.g., within lower x % (x=a specificinteger, 5, 7, 10, . . . )) from the selected resources.

A discovery resource may include one or more resource blocks having thesame size and may be multiplexed within a discovery resource pool in aTDM and/or FDM way.

The reason why the UE selects the resources having a low energy level asthe discovery resources may be considered to mean that UEs do not usethe same D2D discovery resource a lot nearby in the case of resources ofa low energy level. That is, this disprove that the number of UEsperforming D2D discovery procedures that causes interference is not manynearly. Accordingly, if resources having a low energy level are selectedas described above, there is every probability that interference issmall when a discovery message is transmitted.

Furthermore, the reason why a resource having the lowest energy level isnot selected, but discovery resources are randomly selected within apredetermined range (i.e., within lower x %) is that there is apossibility that if a resource having the lowest energy level isselected, several UEs may select the same resource corresponding to thelowest energy level at the same time. That is, a lot of interference maybe caused because UEs select the same resource corresponding to thelowest energy level. Accordingly, a discovery resource may be randomlyselected within a predetermined range (i.e., configuring a candidatepool for selectable resources). In this case, for example, the range ofthe energy level may be variably configured depending on the design of aD2D system.

Furthermore, in the discovery message transmission and reception stepS2105, that is, the last step, the UE transmits and receives discoverymessages based on the discovery resource after a discovery cycle (afterP=10 seconds in FIG. 20) and periodically transmits and receivesdiscovery messages depending on a random resource hopping pattern insubsequent discovery cycles.

Such a D2D discovery procedure continues to be performed even in anRRC_IDLE state not having connection with an eNB as well as in anRRC_CONNECTED state in which the UE has connection with the eNB.

If such a discovery method is taken into consideration, all UEs sensesall resources (i.e., discovery resource pools) transmitted bysurrounding UEs and randomly selects discovery resources from all thesensed resources within a specific range (e.g., within lower x %).

However, the method above has a drawback that a UE has to receive theentire resources that are currently used by the UEs involved in D2Ddiscovery as well as neighboring UEs irrespective of distribution of theneighboring UEs or usage of resources. In other words, since UEs selectdiscovery resources in an arbitrary manner, it is not possible to knowto which position each UE transmits a discovery message. Therefore, itis disadvantageous that all of the UEs have to monitor existence of asignal in the corresponding resources across the whole frequency bandover the whole time period to determine whether to perform detection orto attempt detection.

The received energy level according to the use of discovery resources isnot an absolute value but a relative one. For example, choosing thelower 5% of a distribution is a relative concept that can be interpreteddifferently for each of the UEs. That is, in case the number ofneighboring UEs is large, interference may still be developed even ifthe received energy level is selected as a value within less than 1%; onthe other hand, if very few UEs are found in the vicinity, interferencemay not be developed even if the energy level is selected as a valuebeyond the lower 20%.

The energy level used for distributive resource selection of UEs is aprobabilistic concept, which is employed for selection of discoveryresources, and how many UEs are present currently in the vicinity of aUE to use discovery resources is actually more important than selectingthe energy level as a value within lower percentage. An important issuewhen selecting resources at a low energy level is that the purpose ofresource selection for discovery is to properly select resourcescurrently not used in the vicinity of a UE by selecting resources at alow energy level. Thus, the goal of the scheme above is to discover lotsof UEs by having as many UEs as possible receive a discovery messagebroadcast in the discovery process.

Also, taking into account the mobility of a UE moving around in a randomfashion, a UE may start discovery sensing when there are many other UEsin the surroundings thereof or when there are very few of them. In theend, the energy level of D2D discovery can change in various manneraccording to the discovery time and distribution of neighboring UEs.

To summarize, as described with respect to the method above, it isinefficient to have all of the UEs unconditionally receive and sense thewhole D2D discovery resource pool.

Accordingly, in what follows, the present invention proposes anadaptive, energy-level based sensing method to solve the problem ofsensing the whole discovery resources. In other words, the presentinvention provides a method for adaptively determining a specificresource region to be sensed within a D2D discovery resource pool on thebasis of an energy level detected over a predetermined energy detectioninterval and selecting discovery resources within the specific region.

FIG. 22 illustrates a method for transmitting a D2D discovery messageaccording to one embodiment of the present invention.

With reference to FIG. 22, the UE calculates (namely estimates) theenergy level over an energy detection interval S2201.

To select discovery resources, the UE at first calculates (namelyestimates) the energy level of an energy detection interval by receivingdiscovery messages that neighboring UEs transmit from a predeterminedregion to the energy detection interval instead of sensing the wholediscovery resource pool.

At this time, one or more subframe intervals can be configured as theenergy detection interval, or one or more symbol intervals can beconfigured as the energy detection interval.

For example, in the corresponding discovery resource pool, apredetermined subframe (or symbol) interval can be configured as theenergy detection interval.

Also, the energy detection interval can be configured once within onediscovery period, or it can be set more than once being repeated withinone discovery period.

For example, in case a plurality of discovery resource pools areallocated within one discovery period, a predetermined subframe (orsymbol) interval can be configured as the energy detection interval onlyfor the first discovery resource pool among the plurality of discoveryresource pools. Also, a predetermined subframe (or symbol) interval ofeach discovery resource pool may be configured as the energy detectioninterval.

Also, multiple energy detection intervals may be configured within onediscovery resource pool.

For example, a discovery resource pool can be divided into predeterminedtime periods, and a predetermined subframe (or symbol) interval can beconfigured as an energy detection interval for each predetermined timeperiod. Also, a first symbol interval (or a predetermined number ofsymbol intervals) can be configured as an energy detection interval foreach subframe within the discovery resource pool.

The UE determines a discovery resource region (namely discovery resourcesensing region) on the basis of an energy level calculated (namelyestimated) over the energy detection interval S2203.

In other words, the UE determines the discovery resource region variablyaccording to the amount of discovery resources used by neighboring UEsin the energy detection interval.

At this time, the discovery resource region refers to a candidate regionin which the UE senses discovery messages from neighboring UEs to selectdiscovery resources to be used by the UE and selects discoveryresources. In other words, the discovery resource region refers to aresource region in which UEs grouped according to the energy leveldetected over the energy detection interval perform a discoveryprocedure according to a group-wise manner.

A discovery resource region can comprise a combination of one or more ofthe frequency, time, and spatial region. For example, in case uplinkfrequency band is 10 MHz, the UE sets 10 MHz (or 44 RB) as the discoveryresource region (namely range) if the energy level is larger than apredetermined threshold value according to the energy detection result;if the energy level is less than the predetermined threshold value, theUE sets 5 MHz (or 22 RB) as the discovery resource region (namelyrange). Also, in case 64 subframes are used as a discovery resourcepool, the UE sets the 64 subframes as the discovery resource region(namely interval) if the energy level is larger than a predeterminedthreshold value according to the energy detection result; if the energylevel is less than the predetermined threshold value, the UE may set 32subframes as the discovery resource region (namely interval).

At this time, while determining the size of the discovery resourceregion adaptively according to the energy level, the UE may determinethe position of the discovery resource region arbitrarily. For example,by using the identifier of the UE, position of the discovery resourceregion may be determined in an arbitrary manner.

Also, the start position of the discovery resource region may bepredetermined in the time, frequency, or spatial domain. In other words,while the size of the discovery resource region is determined variablyaccording to the detected energy level, the discovery resource regioncan start from a predetermined position of the frequency, time, orspatial domain. For example, in case the discovery resource region isdetermined adaptively in the frequency domain, the position of thediscovery resource region can be determined by using a Physical ResourceBlock (PRB) index predetermined in the discovery resource pool.

Suppose discovery resources are selected in a random fashion from withinthe lower percentage of the resources in a low energy level as in themethod for selecting discovery resources described above. There can betwo options depending on the frequency: a method for selecting discoveryresources by receiving the whole 10 MHz frequency and a method forselecting discovery resources by receiving 5 MHz frequency selectively.In this case, if there are only a few UEs which use D2D discoveryresources, a sufficient amount of discovery resources are availableirrespective of the frequency range for sensing, and therefore, only thenumber of samples of available discovery resources varies according tothe sensing frequency. In other words, the case of sensing 10 MHzfrequency differs from the case of sensing 5 MHz frequency only by thefact that the number of available discovery resources for the formercase is larger than that for the latter case. High energy levelindicates that there are many UEs in the vicinity while low energy levelindicates that the number of neighboring UEs is small. After all, whatis important in selecting discovery resources is not the lowerpercentage according to a relative energy level but how many neighboringUEs are actually transmitting discovery messages at the time of sensing.

In what follows, described in detail will be a method for a UE todetermine a discovery resource region adaptively on the basis of anenergy level detected over an energy detection interval.

A UE senses discovery resources within a predetermined discoveryresource region and selects resources for discovery message transmission52205. In other words, the UE receives (namely senses) all of thediscovery messages transmitted from the discovery resource regiondetermined in the S2203 step, identifies the resources in a low energylevel, and selects discovery resources that fall within a predeterminedrange (for example, lower x percent of the resources (where x is anarbitrary integer, 5, 7, 10, . . . ) in a random fashion.

The UE transmits a discovery message from the selected resource 52207.And the UE transmits and receives a discovery message periodicallyaccording to a random resource hopping pattern for subsequent discoveryperiods.

Meanwhile, in the S2203 step, the UE may determine a discovery resourceregion on the basis of configuration information about the discoveryresource region received from an eNB and the energy level calculated bythe UE. In this case, before the S2201 step, a step of the UE'sreceiving configuration information about a discovery resource regionfrom the eNB can be additionally included.

The configuration information about the discovery resource regiondenotes the information representing the relationship (namely mappinginformation) between the energy level that the UE has calculated overthe energy detection interval and the discovery resource region. Also,the configuration information may be represented by an equation or arule by which to determine a discovery resource region on the basis ofthe energy level that the UE has calculated.

The discovery resource region can be determined being identified (orbeing separated) in the form of a combination of one or more of thefrequency, time, or spatial domain.

The configuration information about the discovery resource region canspecify only the size of the discovery resource region (namely frequencyband, the number of RBs, or the number of subframes) mapped to theenergy level that the UE has calculated over the energy detectioninterval. For example, in case the uplink frequency band is 10 MHz, ifthe energy level that the UE has calculated exceeds a threshold value,the size of the discovery region is mapped to 10 MHz (or 44 RB); on theother hand, if the energy level is smaller than the threshold value, thesize of the discovery region is mapped to 5 MHz (or 22 RB). In thiscase, the UE may determine the size of the discovery resource regionmapped to the energy level on the basis of the configuration informationabout the discovery resource region, and the position of the discoveryresource region may be determined as a predetermined position or as anarbitrary position determined by the UE as described in detail above.

Also, the configuration information about the discovery resource regioncan specify the size of the discovery resource region (namely frequencyband, the number of RBs, or the number of subframes) and the position ofthe discovery resource region mapped to the energy level that the UE hascalculated over the energy detection interval. In other words, suppose atotal of 44 RBs are used as a discovery resource pool and the discoveryresource region is divided into subregions in the frequency domain. Thenthe size and the position of a discovery resource region ranging fromthe first RB to the 22-th RB; and the size and the position of adiscovery resource region ranging from the first RB to the 44-th RB canbe predetermined. In this case, the UE can determine the size and theposition of the discovery resource region mapped to an energy level onthe basis of the configuration information about the discovery resourceregion.

The discovery resource region can be configured dynamically for eachdiscovery resource pool and can be configured in a semi-static mannerfor one or more discovery periods.

Also, the discovery resource region, being configured in a cell-specificmanner, can be applied commonly to the UEs belonging to thecorresponding cell or can be configured in a UE-specific manner for eachUE.

The configuration information about the discovery resource regionconfigured as described above can be broadcast to the UE periodically assystem information such as System Information Block (SIB) or MasterInformation Block (MIB). Also, the configuration information may betransmitted to the UE through RRC signaling or through a physical layerchannel (for example, PDCCH or PDCCH).

FIG. 23 illustrates a method for adaptively determining a discoveryresource region in the frequency domain according to one embodiment ofthe present invention.

In FIG. 23, small rectangles represent discovery resources currentlyused by other UEs, and different patterns applied for the rectanglesindicate that discovery resources are used by different UEs.

FIG. 23 assumes that a discovery resource pool 2301 comprises 44 RBpairs (namely 10 MHz) in the frequency domain while it comprises 64subframes in the time domain. It is further assumed that one or moresubframes (or symbols) of the discovery resource pool 2301 comprise anenergy detection interval 2303.

As shown in FIG. 23, UE1 and UE2 calculate (namely estimate) the energylevel over the energy detection interval 2303 and determines differentdiscovery resource regions (namely sensing ranges) 2305, 2307 in thefrequency domain according to the calculated energy levels.

Even if the UE1 and the UE2 calculate the energy level over the sameenergy detection interval 2303, the energy levels calculated by the UE1and the UE2 can be different from each other depending on theirpositions.

At this time, it is assumed that the UE1 and the UE2 calculate (namelyestimate) the energy level over the energy detection interval 2303, andthe energy level calculated (namely estimated) by the UE1 is less than apredetermined threshold value while the energy level calculated (namelyestimated) by the UE2 is larger than the predetermined threshold value.

In this case, the UE1 has only a few neighboring UEs, the wholediscovery resource region (namely sensing range) 2305 is set to besmaller than 10 MHz, and discovery resources are selected from among theconfigured discovery resource region. Meanwhile, the UE2 has a largenumber of neighboring UEs, and different from the UE1, discoveryresources can be selected by configuring the discovery resource region(namely sensing range) 2307 to be larger than that of the UE1 (forexample, the whole frequency band).

The UE1 and the UE2 determine the size of their discovery resourceregion according to the energy level estimated over the energy detectioninterval 2303, but the position of the discovery resource region may bedetermined in a random fashion. At this time, the position of thediscovery resource region can be determined in a random fashion by usingthe identifier of the UE (for example, C-RNTI). For example, from thewhole discovery resource pool, the position from which the discoveryresource region starts (for example, the first PRB index, the 11-th PRBindex, the 22^(nd) PRB index, and the 33^(rd) PRB index of the discoveryresource pool) can be determined beforehand, and the position from whichthe discovery resource region starts can be determined by applyingmodular-4 operation to the UE identifier.

Also, the start position of the discovery resource region can be fixed.For example, the position of the discovery resource region can bedetermined as the one starting from a predetermined position in thediscovery resource pool (for example, the first PRB index of thediscovery resource pool).

Meanwhile, FIG. 23 illustrates a case where the discovery resourceregion of the UE1 (namely UE1 sensing range) 2305 does not overlap withthe discovery resource region of the UE2 (namely UE2 sensing range)2307; however, the discovery resource region of the UE1 (namely UE1sensing range) 2305 can be made to overlap with the discovery resourceregion of the UE2 (namely UE2 sensing range) 2307.

FIG. 24 illustrates a method for adaptively determining a discoveryresource region in the time domain according to one embodiment of thepresent invention. In FIG. 24, small rectangles represent discoveryresources currently used by other UEs, and different patterns appliedfor the rectangles indicate that discovery resources are used bydifferent UEs.

FIG. 24 assumes that a discovery resource pool 2401 comprises 44 RBpairs (namely 10 MHz) in the frequency domain while it comprises 64subframes in the time domain. It is further assumed that one or moresubframes (or symbols) of the discovery resource pool 2401 comprise anenergy detection interval 2403.

As shown in FIG. 24, UE1 and UE2 calculate (namely estimate) the energylevel over the energy detection interval 2403 and determines differentdiscovery resource regions (namely sensing ranges) 2405, 2407 in thetime domain according to the calculated energy levels.

At this time, it is assumed that the UE1 and the UE2 calculate (namelyestimate) the energy level over the energy detection interval 2403, andthe energy level calculated (namely estimated) by the UE1 is less than apredetermined threshold value while the energy level calculated (namelyestimated) by the UE2 is larger than the predetermined threshold value.

In this case, the UE1 has only a few neighboring UEs, the wholediscovery resource region (namely sensing range) 2405 is set to besmaller than 64 subframes at maximum, and discovery resources areselected from among the configured discovery resource region. Meanwhile,the UE2 has a large number of neighboring UEs, and different from theUE1, discovery resources can be selected by configuring the discoveryresource region (namely sensing range) 2407 to be larger than that ofthe UE1 (for example, the discovery resource pool time interval).

The UE1 and the UE2 determine the size of their discovery resourceregion according to the energy level estimated over the energy detectioninterval 2403, but the position of the discovery resource region may bedetermined in a random fashion. At this time, the position of thediscovery resource region can be determined in a random fashion by usingthe identifier of the UE (for example, C-RNTI). For example, from thewhole discovery resource pool, the position from which the discoveryresource region starts (for example, the first subframe index, the 16-thsubframe index, the 32^(nd) subframe index, and the 48-th subframe indexof the discovery resource pool) can be determined beforehand, and theposition from which the discovery resource region starts can bedetermined by applying modular-4 operation to the UE identifier.

Also, the start position of the discovery resource region can be fixed.For example, the position of the discovery resource region can bedetermined as the one starting from a predetermined position in thediscovery resource pool (for example, the first subframe index after theenergy detection interval 2403 of the discovery resource pool).

Meanwhile, FIG. 24 illustrates a case where the discovery resourceregion of the UE1 (namely UE1 sensing range) 2405 does not overlap withthe discovery resource region of the UE2 (namely UE2 sensing range)2407; however, the discovery resource region of the UE1 (namely UE1sensing range) 2405 can be made to overlap with the discovery resourceregion of the UE2 (namely UE2 sensing range) 2407.

Through the method above, namely according to the distribution ofneighboring UEs, the discovery message reception range (or interval) isreduced so that resource sensing power for transmitting discoverymessages of UEs can be saved. Furthermore, if the discovery messagereception range (or interval) is set to be small, processing overheadfrom selecting sensed resources by classifying them according to energylevels within a predetermined range (for example, within a lowerpercentage) can be reduced, and fast sensing and selection of discoveryresources is possible. The numbers introduced above are only examplesfor the purpose of description and can be set differently according tovarious other methods.

FIG. 25 illustrates an energy detection interval set in the time domainin a repetitive manner according to one embodiment of the presentinvention.

In FIG. 25, small rectangles represent discovery resources currentlyused by other UEs, and different patterns applied for the rectanglesindicate that discovery resources are used by different UEs.

FIG. 25 assumes that a discovery resource pool 2501 comprises 44 RBpairs (namely 10 MHz) in the frequency domain while it comprises 64subframes in the time domain.

As shown in FIG. 25, a plurality of energy detection intervals 2503 canbe set up in the discovery resource pool 2501. In other words, the wholeresource pool 2501 is divided into a plurality of time slots (in thecase of FIG. 25, 3), and one or more subframes (or symbols) can beconfigured as an energy detection interval 2503 in each time slot.Through this scheme, UEs can sense resources for transmitting discoverymessages sequentially in the respective energy detection intervals 2503and determine discovery resources adaptively for the respective timeslots according to the sensed energy level. In other words, for therespective time slots, discovery resource regions can be determinedindependently from each other. And the UEs can select discoveryresources in the discovery resource regions determined.

In this case, if a random discovery message transmission pattern isused, a specific hopping pattern may cause a large amount of discoverymessage transmission in the 3rd slot, whereby the energy level can beincreased abruptly.

In this case, as shown in FIG. 25, even if discovery messages areabundantly used suddenly in the 3rd time slot to increase the energylevel, the sensing interval (namely discovery resource region) can stillbe configured to be small for the first and the second time slot whilethe discovery message sensing interval (namely discovery resourceregion) can be configured to be large for the 3rd time slot in order toaccommodate the discovery message energy level sent from thesurroundings. Therefore, the UE can select the discovery resources of alow energy level from within the sensing interval configured to be large(namely discovery resource region), which will be described in moredetail below with reference to FIGS. 26 and 27.

FIG. 26 illustrates a method for adaptively determining a discoveryresource region in the frequency domain in case an energy detectioninterval is set repeatedly in the time domain according to oneembodiment of the present invention.

With reference to FIG. 26, UE1 calculates (namely estimates) energylevels of the energy detection intervals 2603, 2605, 2607 set up in therespective time slots and determines discovery resource regions (namelysensing ranges) 2609, 2611, 2613 different from each other in thefrequency domain within the respective time slots according to thecalculated energy levels.

At this time, based on the energy levels calculated (namely estimated)for the respective energy detection intervals 2603, 2605, 2607, UE1assumes that the energy levels calculated (namely estimated) over thefirst 2603 and the second energy detection interval 2605 are less than apredetermine threshold value while the energy level calculated (namelyestimated) over the third energy detection interval 2607 is larger thanthe predetermined threshold value.

In this case, determining that very few neighboring UEs exist in thefirst and the second time slot, the UE1 can configure the discoveryresource region (namely sensing range) 2609, 2611 to be smaller than 10MHz at maximum and select discovery resources from within the configureddiscovery resource region. On the other hand, determining that a largenumber of neighboring UEs exist in the 3rd time slot, the UE1 canconfigure the discovery resource region (namely sensing range) 2613 tobe larger (for example, the whole frequency band) than the discoveryresource regions 2609, 2611 of the first/second time slot and select thediscovery resources from within the configured discovery resourceregion.

In other words, the whole discovery resource pool can be divided inunits of time slots, and discovery resource regions (namely sensingranges) for UEs can be configured differently from each other in thefrequency domain according to the energy detection results over therespective time slots.

At this time, although the UE1 determines the size of each discoveryresource region 2609, 2611, 2613 according to the energy level estimatedover each energy detection interval 2603, 2605, 2607, as described abovewith reference to FIG. 23, the position of each discovery resourceregion can be determined in a random fashion. For example, the positionof a discovery resource region can be determined by using the UEidentifier. Also, the start position of a discovery resource region maybe fixed. For example, a discovery resource region can start from theposition of a predetermined PRB index.

FIG. 27 illustrates a method for adaptively determining a discoveryresource region in the time domain in case an energy detection intervalis set repeatedly in the time domain according to one embodiment of thepresent invention.

With reference to FIG. 27, UE1 calculates (namely estimates) energylevels of the energy detection intervals 2703, 2705, 2707 set up in therespective time slots and determines discovery resource regions (namelysensing ranges) 2709, 2711, 2713 different from each other in the timedomain within the respective time slots according to the calculatedenergy levels.

At this time, based on the energy levels calculated (namely estimated)for the respective energy detection intervals 2703, 2705, 2707, UE1assumes that the energy levels calculated (namely estimated) over thefirst 2703 and the second energy detection interval 2705 are less than apredetermine threshold value while the energy level calculated (namelyestimated) over the third energy detection interval 2707 is larger thanthe predetermined threshold value.

In this case, determining that very few neighboring UEs exist in thefirst and the second time slot, the UE1 can configure the discoveryresource region (namely sensing range) 2709, 2711 to be smaller than themaximum time slot interval and select discovery resources from withinthe configured discovery resource region. On the other hand, determiningthat a large number of neighboring UEs exist in the 3rd time slot, theUE1 can configure the discovery resource region (namely sensing range)2713 to be larger (for example, the whole frequency band) than thediscovery resource regions 2709, 2711 of the first/second time slot andselect the discovery resources from within the configured discoveryresource region.

In other words, the whole discovery resource pool can be divided inunits of time slots, and discovery resource regions (namely sensingranges) for UEs can be configured differently from each other in thetime domain according to the energy detection results over therespective time slots.

At this time, although the UE1 determines the size of each discoveryresource region 2709, 2711, 2713 according to the energy level estimatedover each energy detection interval 2703, 2705, 2707, as described abovewith reference to FIG. 24, the position of each discovery resourceregion can be determined in a random fashion. For example, the positionof a discovery resource region can be determined by using the UEidentifier. Also, the start position of a discovery resource region maybe fixed. For example, a discovery resource region can start from theposition of a predetermined subframe index.

Meanwhile, referring again to FIG. 25, by performing sensing over onlypart of the time slots and selecting discovery resources, the UE may notperform sensing over the remaining time slots, which will be describedin more detail below with reference to FIG. 28.

FIG. 28 illustrates a method for adaptively determining a discoveryresource region in the time domain in case an energy detection intervalis set repeatedly in the time domain according to one embodiment of thepresent invention.

With reference to FIG. 28, from the energy detection result over anenergy detection interval 2803 set up in the first time slot, the UE candetermine that there are only a few neighboring UEs since the discoverymessage energy level from the neighboring UEs is very low (for example,less than a predetermined threshold value). In this case, the UE canselect discovery resources from the first time slot, but may not performsensing over the remaining second and third time slot in search of theresources for transmitting a discovery message.

In this way, since the UE selects discovery resources directly from thefirst time slot and does not perform sensing during the other timeslots, energy can be saved.

Also, different from the embodiment of FIG. 28, from the energydetection result over the energy detection interval 2803 set up in thefirst time slot, the UE can determine that there are quite a fewneighboring UEs since the discovery message energy level from theneighboring UEs is high (for example, more than a predeterminedthreshold value). In this case, the UE can perform energy detectionagain over the energy detection interval 2803 set up in the second timeslot. And from the energy detection result over the energy detectioninterval 2803 set up in the second time slot, the UE can determine thatthere are very few neighboring UEs since the discovery message energylevel is too low (for example, less than a predetermined thresholdvalue). In this case, the UE can select discovery resources from thesecond time slot, but may not perform sensing over the remaining thirdtime slot in search of the resources for transmitting a discoverymessage.

Also, the sensing interval (namely, the number of time slots) todiscover resources for the UE to transmit a discovery message can bedetermined according to the energy level measured over the energydetection interval 2803 set up in the first time slot. For example, ifthe energy level measured over the energy detection interval 2803 set upin the first time slot is less than a predetermined first thresholdvalue, the UE can perform sensing the resources for transmission of adiscovery message only over the first time slot. And if the energy levelmeasured over the energy detection interval 2803 set up in the firsttime slot is larger than the predetermined first threshold value butless than a predetermined second threshold value, the UE can performsensing the resources for transmission of a discovery message over thefirst and the second time slot. And if the energy level measured overthe energy detection interval 2803 set up in the first time slot islarger than the predetermined second threshold value, the UE can performsensing the resources for transmission of a discovery message over thefirst, the second, and the third time slot.

As described above, if the UE selects discovery resources from the firsttime slot, the energy consumed at the time of searching for discoveryresources can be saved by as much as the time slot (1/slot) by which thewhole discovery resource pool is divided. At this time, although moreenergy can be as the number of time slots is increased, it is preferablethat the number of time slots should be determined in a proper mannerwithin the whole discovery resource pool by taking into account theminimum number of sensing resources required to select appropriatediscovery resources through sensing. In the case of FIG. 28, if it isassumed that three time slots are used and a specific UE completessensing the resources for transmission of a discovery message over thefirst time slot, the energy consumed for D2D discovery sensing can bereduced by three times. The aforementioned number is only an example todescribe the embodiment, which can be determined in various other ways.

Also, the method for adaptively sensing resources for transmission of adiscovery message on the basis of time slots according to the presentinvention can reduce the delay generated from the D2D discoveryprocedure.

First, suppose a time slot of 64 ms from the whole discovery periodlasting 10 s is allocated to the D2D discovery resource pool. At thistime, according to an existing D2D discovery method, if the time atwhich the UE is powered on and starts D2D discovery corresponds to atime interval for cellular communication rather than the time intervalof 64 ms for which the periodic D2D discovery resource pool is set up,the UE starts the D2D discovery at the next discovery period.

However, the time at which the UE is powered on and starts D2D discoverycorresponds to a time interval for which the D2D discovery resource poolis set up. According to the example above, this time slot falls within64 ms from within the whole discovery period of 10 s for which the D2Ddiscovery resource pool is set up (namely 64 ms/10 s), yielding aprobability of 0.64%. In this case, UEs can start sensing the resourcesimmediately in the time slot for which the D2D discovery resource poolis set up.

However, even for this case, too, according to the existing discoverymethod, if sensing is started in the middle of the discovery resourcepool, since the UE is unable to receive discovery messages from otherUEs across the whole discovery resource pool, the UE becomes unable toselect the discovery resources. Therefore, in order for the UE toreceive discovery messages from other UEs across the whole discoveryresource pool, the UE waits for another 10 s of the next discoveryperiod and selects discovery resources by sensing them over the wholediscovery resource pool during 64 ms. After all, the UEs startingsensing the resources in the middle of 64 ms experience a very longdelay of 10 s during the D2D discovery procedure.

On the other hand, as described in the embodiment of FIG. 25, accordingto the resource sensing method for transmitting a discovery message onthe basis of time slots according to the present invention, the UE canselect discovery resources even if the UE does not receive discoverymessages of neighboring UEs across the whole discovery resource pool,which will be described below with reference to FIG. 29.

FIG. 29 illustrates a method for adaptively determining a discoveryresource region in the time domain in case an energy detection intervalis set repeatedly in the time domain according to one embodiment of thepresent invention.

FIG. 29 assumes that the UE is powered on and starts sensing for D2ddiscovery from the second time slot.

In this way, even if the UE has started sensing for D2D discovery fromthe second time slot (namely from the middle of the discovery resourcepool), the UE can perform sensing from the third time slot andimmediately select discovery resources without receiving the wholediscovery resource pool in case there are only a few neighboring UEs. Inother words, since the UE selects discovery resources even when the UEperforms sensing of only part of the discovery resource pool, the UE canreduce the delay of waiting for the next discovery period. The numbersintroduced above are only examples for the purpose of description andcan be set differently according to various other methods.

In this way, the present invention can configure the discovery resourceregion (namely the resource sensing region for transmission of adiscovery message) adaptively in the time or frequency domain on thebasis of the energy level measured over the energy detection interval.

According to the adaptive sensing method of the present invention, thefrequency/time interval over which the UE performs sensing can bereduced variably on the basis of the amount of resources used accordingto a relative distribution of other UEs in the vicinity of the UE, andthus the sensing power of the UEs can be reduced. Also, since thefrequency/time interval for sensing is reduced, overhead generated inthe processing stage can be reduced in an effective manner.

Also, since the UE operates on the basis of time slots and doesn'tnecessarily have to perform sensing whole interval in case that the UEemploys an adaptive sensing method based on time slots according to thepresent invention, the UE can not only reduce the energy consumed forD2D discovery but reduce a delay by selectively selecting discoveryresources even if UEs start sensing from the middle of the discoveryresource pool; therefore the UE becomes capable of selecting discoveryresources and transmitting a discovery message more quickly thanexisting methods.

To be more specific, if the energy level is low because of the energydetection performed over a predetermined specific resource region (forexample, one or more subframes or one or more symbols), it indicatesthat only a few UEs are transmitting discovery messages in the vicinityof the UE. In this case, the probability of collision with other UEs canbe small even if the UEs select resources in a random fashion andtransmit discovery messages. However, as described above, it ispreferable that the UEs identify resources of low energy levels fromamong sensed resources, select one from among the resources fallingwithin a predetermined range of the energy level in a random fashion,and transmit discovery messages by using the selected resource.

However, estimating energy by sensing the whole bandwidth or the wholetime interval (discovery 1 period) to find resources with an energylevel within a predetermined range (for example, less than lower x %) isinefficient from a standpoint of power consumption. To alleviate thisproblem, in case the detected energy over a particular region is small,the present invention still obtains the same effect by performing energyestimation over only part of the bandwidth or the interval withoutnecessarily performing energy estimation over the whole range to find aresource region with an energy level less than x %; selecting resourceswith energy levels less than x % from within the part of the wholedomain (even a small number of samples are sufficient for this purpose);and transmitting a discovery message by selecting one from among theselected resources. Moreover, since the energy sensing range is reducedconsiderably, the present invention is more advantageous in terms ofpower consumption. On the contrary, if energy detected over a particularregion becomes large, energy sensing can be performed over the wholefrequency or time region. However, it should be noted that even in thiscase, power consumption can be improved by adjusting the energy sensingregion variably in a step-wise manner according to the energy valuedetected over a particular region.

With reference to the embodiments of the present invention above, amethod for adaptively configuring a discovery resource region in thetime domain or frequency domain has been described. However, the methodabove is only an example introduced for the purpose of description, andthe present invention is not limited to the description above. In otherwords, a discovery resource region can also be set up adaptively bycombining the frequency and the time domain according to the presentinvention in the same way as described above.

Also, the discovery resource region can still be set up over the spatialdomain by applying the same method for setting up a discovery resourceregion in the frequency and time domain. Also, the discovery resourceregion can also be set up by combining the spatial domain with thefrequency domain in the same way as the method for setting up adiscovery resource region by combining the time and frequency domain.Furthermore, operations according to the present invention may beperformed by combining other domains (for example, UE IDs, cell IDs, andso on) in addition to the time, frequency, and spatial domain.

General Wireless Communication Device to which an Embodiment of thePresent Invention May be Applied

FIG. 30 illustrates a block diagram of a wireless communication deviceaccording to an embodiment of the present invention.

Referring to FIG. 30, the wireless communication system includes an eNB3010 and a plurality of UEs 3020 placed within the area of the eNB 3010.

The eNB 3010 includes a processor 3011, memory 3012, and a RadioFrequency (RF) unit 3013. The processor 3011 implements the functions,processes and/or methods proposed with reference to FIGS. 1 to 29. Thelayers of the radio interface protocol may be implemented by theprocessor 3011. The memory 3012 is connected to the processor 3011 andstores various types of information for driving the processor 3011. TheRF unit 3013 is connected to the processor 3011 and sends and/orreceives radio signals.

The UE 3020 includes a processor 3021, memory 3022, and an RF unit 3023.The processor 3021 implements the functions, processes and/or methodsproposed with reference to FIGS. 1 to 29. The layers of the radiointerface protocol may be implemented by the processor 3021. The memory3022 is connected to the processor 3021 and stores various types ofinformation for driving the processor 3021. The RF unit 3023 isconnected to the processor 3021 and sends and/or receives radio signals.

The memory 3012, 3022 may be placed inside or outside the processor3011, 3021 and may be connected to the processor 3011, 3021 bywell-known various means. Furthermore, the eNB 3010 and/or the UE 3020may have a single antenna or multiple antennas.

Hereinafter, detailed embodiments of the present invention are describedin detail with reference to the accompanying drawings. Each of elementsor characteristics may be considered to be optional unless otherwisedescribed explicitly. Each element or characteristic may be implementedin such a way as not to be combined with other elements orcharacteristics. Furthermore, some of the elements and/or thecharacteristics may be combined to form an embodiment of the presentinvention. Order of operations described in connection with theembodiments of the present invention may be changed. Some of theelements or characteristics of an embodiment may be included in anotherembodiment or may be replaced with corresponding elements orcharacteristics of another embodiment. It is evident that in the claims,one or more embodiments may be constructed by combining claims nothaving an explicit citation relation or may be included as one or morenew claims by amendments after filing an application.

An embodiment of the present invention may be implemented by variousmeans, for example, hardware, firmware, software or a combination ofthem. In the case of implementations by hardware, an embodiment of thepresent invention may be implemented using one or moreApplication-Specific Integrated Circuits (ASICs), Digital SignalProcessors (DSPs), Digital Signal Processing Devices (DSPDs),Programmable Logic Devices (PLDs), Field Programmable Gate Arrays(FPGAs), processors, controllers, microcontrollers and/ormicroprocessors.

In the case of implementations by firmware or software, an embodiment ofthe present invention may be implemented in the form of a module,procedure, or function for performing the aforementioned functions oroperations. Software code may be stored in the memory and driven by theprocessor. The memory may be placed inside or outside the processor, andmay exchange data with the processor through a variety of known means.

It is evident to those skilled in the art that the present invention maybe materialized in other specific forms without departing from theessential characteristics of the present invention. Accordingly, thedetailed description should not be construed as being limitative fromall aspects, but should be construed as being illustrative. The scope ofthe present invention should be determined by reasonable analysis of theattached claims, and all changes within the equivalent range of thepresent invention are included in the scope of the present invention.

INDUSTRIAL APPLICABILITY

The method for transmitting a discovery message in a wirelesscommunication system according to an embodiment of the present inventionhas been illustrated as being applied to 3GPP LTE/LTE-A systems, but maybe applied to various wireless communication systems other than the 3GPPLTE/LTE-A systems.

1. A method for transmitting a discovery message in a wireless communication system supporting communication between user equipments (UEs), comprising: estimating, by a UE, an energy level over an energy detection interval configured within a discovery resource pool; determining, by the UE, a discovery resource region of the UE on the basis of the estimated energy level; selecting, by the UE, a discovery resource for transmitting a discovery message within the determined discovery resource region; and transmitting, by the UE, the discovery message from the selected discovery resource.
 2. The method of claim 1, wherein the discovery message resource region is adaptively configured to one region or a combination of two more regions from among frequency domain, time domain, and spatial domain within the discovery resource pool.
 3. The method of claim 1, wherein the UE senses the determined discovery resource region and arbitrarily selects the discovery resource from among the resources of which the energy level falls within a predetermine range.
 4. The method of claim 1, wherein the energy detection interval comprises one or more subframes, or one or more symbol intervals.
 5. The method of claim 1, wherein size of the discovery resource region is determined on the basis of the estimated energy level, and a location of the discovery resource region is randomly determined by using the UE identifier.
 6. The method of claim 1, wherein the discovery resource pool is divided into a plurality of time slots, and the energy detection interval is configured for each of the plurality of time slots.
 7. The method of claim 6, wherein the discovery resource region is determined independently for each of the plurality of time slots.
 8. The method of claim 7, wherein the discovery resource is selected by sensing only part of the discovery resource regions from among the discovery resource regions configured for each of the plurality of time slots.
 9. The method of claim 7, wherein, in case the UE starts sensing one of the discovery resource regions from among the discovery resource regions configured for each of the plurality of time slots, the discovery resource is selected within the discovery resource region next to the discovery resource region over which the UE has started sensing.
 10. A user equipment (UE) transmitting a discovery message in a wireless communication system supporting communication between UEs, comprising: a Radio Frequency (RF) unit for transmitting and receiving a radio signal; and a processor, wherein the processor is configured to estimate an energy level over an energy detection interval configured within a discovery resource pool, to determine a discovery resource region of the UE on the basis of the estimated energy level, to select a discovery resource for transmitting a discovery message within the determined discovery resource region, and to transmit the discovery message from the selected discovery resource. 